diff --git a/district-scripts/SWF/GateFlow5.py b/district-scripts/SWF/GateFlow5.py
index d0d4e3f..affa042 100644
--- a/district-scripts/SWF/GateFlow5.py
+++ b/district-scripts/SWF/GateFlow5.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,30 +67,21 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
-    # the gate flow calculations requires a start and end time.
-    # here we create a java Calendar object that will be used to create the start Date
-    startCal = Calendar.getInstance(timeZone)
-    # startCal.clear()
-    startCal.add(Calendar.DAY_OF_MONTH, -8)
-    startCal.set(Calendar.HOUR_OF_DAY, 0)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-    # startCal.set(Calendar.YEAR, 2015)
-    # startCal.set(Calendar.MONTH, 9)
-
-    # create a java Calendar object that will be used to create the end Date
-    endCal = Calendar.getInstance(timeZone)
-    # endCal.clear()
-    endCal.add(Calendar.DAY_OF_MONTH, 1)
-    endCal.set(Calendar.HOUR_OF_DAY, 0)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    # endCal.set(Calendar.YEAR, 2015)
-    # endCal.set(Calendar.MONTH, 11)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+
+    # start of the day 8 days ago, local midnight
+    start_date_dt = (datetime.now(central) - timedelta(days=8)).replace(
+        hour=0, minute=0, second=0, microsecond=0
+    )
+    # end of today: tomorrow's local midnight
+    end_date_dt = start_date_dt + timedelta(days=9)
+    # Dates can be adjusted with normal datetime arithmetic/replace, e.g.:
+    #   start_date_dt = start_date_dt.replace(year=2015, month=10)  # month is 1-indexed here
+
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
 
     officeID = "SWF"
 
@@ -98,7 +91,7 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
     # By setting the following parameter to True, the following flow groups in the list FlowGroupList will all be calculated. Items can be commented out
     # or commented back in individually. To turn this option off, set the following parameter to False. User can determine which flow group they want to calculate
 
@@ -189,10 +182,10 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     if calculateAllFlowGroups:
         for location in FlowGroupList:
             print("Now Running", location, "GROUP")
-            compute_All_Flowgroups(officeID, location, startCal, endCal)
+            compute_All_Flowgroups(officeID, location, start_date, end_date)
 
-    compute_Single_Flowgroup(officeID, "JSPT2", startCal, endCal, "Turbine1")
-    compute_Single_Flowgroup(officeID, "JSPT2", startCal, endCal, "Turbine2")
+    compute_Single_Flowgroup(officeID, "JSPT2", start_date, end_date, "Turbine1")
+    compute_Single_Flowgroup(officeID, "JSPT2", start_date, end_date, "Turbine2")
 
 
     #if calculateSingleFlowGroups:
diff --git a/district-scripts/SWF/GateFlow_MonthlyPumpBackFill.py b/district-scripts/SWF/GateFlow_MonthlyPumpBackFill.py
index 7bb1ae5..7a0e269 100644
--- a/district-scripts/SWF/GateFlow_MonthlyPumpBackFill.py
+++ b/district-scripts/SWF/GateFlow_MonthlyPumpBackFill.py
@@ -2,29 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -64,41 +67,22 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # the gate flow calculations requires a start and end time.
-    # here we create a java Calendar object that will be used to create the start Date
-    startCal = Calendar.getInstance()
-    # startCal.clear()
-    startCal.set(Calendar.HOUR, 0)  ### set startCal hour/minute/second/millisecond to 0 for midnight
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-    startCal.add(Calendar.YEAR, -1)  ### go back one year to today
-    startCal.set(Calendar.MONTH, 9)  ### change month to month 9 (october)
-    startCal.set(Calendar.DAY_OF_MONTH, 1)   ### change start date to start of the month day 1
-
-    getYear = startCal.get(Calendar.YEAR)  ### get value of startCal year/month/day to print and to initilize endCal
-    getMonth = startCal.get(Calendar.MONTH)
-    getDayofMonth = startCal.get(Calendar.DAY_OF_MONTH)
-
-    # create a java Calendar object that will be used to create the end Date
-    endCal = Calendar.getInstance()
-    # endCal.clear()
-    endCal.set(Calendar.HOUR, 0)  ### set endCal hour/minute/second/millisecond to 0 for midnight
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    ###endCal will be set to current date unless reset with the following 4 lines
-    #endCal.set(Calendar.YEAR, getYear)  ### set endCal year same as startCal
-    #endCal.set(Calendar.MONTH, getMonth)  ### set endCal month same as startCal
-    #endCal.add(Calendar.MONTH, 12)  ##add 1 month to startcal month
-    #endCal.set(Calendar.DAY_OF_MONTH, 1)  ### set to day one 
-
-    ### time window starts 01Feb2019(one year ago) and ends 01Mar2019 (one year ago plus one month)
-
-    getEndDay = endCal.get(Calendar.DAY_OF_MONTH)
-    getEndYear = endCal.get(Calendar.YEAR)
-    getEndMonth = endCal.get(Calendar.MONTH)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time. (The previous Calendar.getInstance()
+    # calls here had no explicit timezone and silently depended on whatever
+    # timezone the host happened to be configured with.)
+    central = ZoneInfo("America/Chicago")
+    today = datetime.now(central)
+
+    # start: October 1st of last year, at midnight
+    start_date_dt = today.replace(
+        year=today.year - 1, month=10, day=1, hour=0, minute=0, second=0, microsecond=0
+    )
+    # end: today, at midnight
+    end_date_dt = today.replace(hour=0, minute=0, second=0, microsecond=0)
 
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
 
     officeID = "SWF"
 
@@ -108,7 +92,7 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
     # By setting the following parameter to True, the following flow groups in the list FlowGroupList will all be calculated. Items can be commented out
     # or commented back in individually. To turn this option off, set the following parameter to False. User can determine which flow group they want to calculate
     # by changing the "flowGroup" variable.
@@ -191,17 +175,17 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     if calculateSingleFlowGroups:
         for location in locationList:
             print("Now Running", location, "SINGLE")
-            #compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupGate)
-            #compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupTotal)
-            #compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupTurbine)
-            #compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupUncontrol)
-            #compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupPumpOutBelow)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupPumpOut)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupPumpIn)
+            #compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupGate)
+            #compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupTotal)
+            #compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupTurbine)
+            #compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupUncontrol)
+            #compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupPumpOutBelow)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupPumpOut)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupPumpIn)
     if calculateAllFlowGroups:
         for location in FlowGroupList:
             print("Now Running", location, "GROUP")
-            #compute_All_Flowgroups(officeID, location, startCal, endCal)
+            #compute_All_Flowgroups(officeID, location, start_date, end_date)
 
 
 
diff --git a/district-scripts/SWF/GateFlow_PumpBackFill.py b/district-scripts/SWF/GateFlow_PumpBackFill.py
index bc58977..bdedf10 100644
--- a/district-scripts/SWF/GateFlow_PumpBackFill.py
+++ b/district-scripts/SWF/GateFlow_PumpBackFill.py
@@ -2,29 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -64,28 +67,20 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # the gate flow calculations requires a start and end time.
-    # here we create a java Calendar object that will be used to create the start Date
-    startCal = Calendar.getInstance()
-    # startCal.clear()
-    startCal.add(Calendar.DAY_OF_MONTH, -1)
-    startCal.set(Calendar.HOUR, 0)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-    # startCal.set(Calendar.YEAR, 2015)
-    # startCal.set(Calendar.MONTH, 9)
-
-    # create a java Calendar object that will be used to create the end Date
-    endCal = Calendar.getInstance()
-    # endCal.clear()
-    endCal.add(Calendar.DAY_OF_MONTH, 0)
-    endCal.set(Calendar.HOUR, 0)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    # endCal.set(Calendar.YEAR, 2015)
-    # endCal.set(Calendar.MONTH, 11)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time. (The previous Calendar.getInstance()
+    # calls here had no explicit timezone and silently depended on whatever
+    # timezone the host happened to be configured with.)
+    central = ZoneInfo("America/Chicago")
+    today_midnight = datetime.now(central).replace(hour=0, minute=0, second=0, microsecond=0)
+
+    # start: yesterday, at midnight
+    start_date_dt = today_midnight - timedelta(days=1)
+    # end: today, at midnight
+    end_date_dt = today_midnight
+
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
 
     officeID = "SWF"
 
@@ -95,7 +90,7 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
     # By setting the following parameter to True, the following flow groups in the list FlowGroupList will all be calculated. Items can be commented out
     # or commented back in individually. To turn this option off, set the following parameter to False. User can determine which flow group they want to calculate
     # by changing the "flowGroup" variable.
@@ -156,36 +151,36 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     if calculateSingleFlowGroups:
         for location in locationList:
             print("Now Running", location, "SINGLE")
-            #compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupGate)
-            #compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupTotal)
-            #compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupTurbine)
-            #compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupUncontrol)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupPumpOutBelow)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupPumpOut)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupPumpIn)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupNTMWD)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupUTRWD) 
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupSS)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupIrving) 
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupLewisville)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupUTRWD_Out)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupUTRWD_In)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupIrv)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupDenton)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupBenbrook)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupTRWD)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupWeatherford) 
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupGeorgetown)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupRound_Rock) 
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupBrushy_Ck)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupNTMWD_LVN)
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupCooper) 
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupEast_Fork) 
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroupTawakoni)
+            #compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupGate)
+            #compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupTotal)
+            #compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupTurbine)
+            #compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupUncontrol)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupPumpOutBelow)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupPumpOut)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupPumpIn)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupNTMWD)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupUTRWD) 
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupSS)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupIrving) 
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupLewisville)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupUTRWD_Out)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupUTRWD_In)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupIrv)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupDenton)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupBenbrook)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupTRWD)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupWeatherford) 
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupGeorgetown)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupRound_Rock) 
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupBrushy_Ck)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupNTMWD_LVN)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupCooper) 
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupEast_Fork) 
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroupTawakoni)
     if calculateAllFlowGroups:
         for location in FlowGroupList:
             print("Now Running", location, "GROUP")
-            #compute_All_Flowgroups(officeID, location, startCal, endCal)
+            #compute_All_Flowgroups(officeID, location, start_date, end_date)
 
 
 
diff --git a/district-scripts/SWF/GateSettings.py b/district-scripts/SWF/GateSettings.py
index b94e476..2c714a5 100644
--- a/district-scripts/SWF/GateSettings.py
+++ b/district-scripts/SWF/GateSettings.py
@@ -2,11 +2,13 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    # the java Calendar class is used to create java Date objects
-    from java.util import Calendar
     from usace.rowcps.headless import LoggingOptions
 
+
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -42,42 +44,34 @@ def run_calculations(registry):
     # this gets a scriptable Gate Settings object
     gateSettings = registry.getCalculation(1.0, "Gate Settings")
 
-    # configure the start calendar
-    startCal = Calendar.getInstance()
-    #startCal.clear()
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    startCal.set(Calendar.HOUR, 0)        ######use Calendar.HOUR_OF_DAY
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-    # create a java Calendar object that will be used to create the end Date
-    endCal = Calendar.getInstance()
-    endCal.add(Calendar.DAY_OF_MONTH, 1)
-    endCal.set(Calendar.HOUR, 0)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    #endCal.clear()
-    #endCal.set(Calendar.YEAR, 2016)
-    #endCal.set(Calendar.MONTH, 4)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time. (The previous Calendar.getInstance()
+    # calls here had no explicit timezone and silently depended on whatever
+    # timezone the host happened to be configured with.)
+    central = ZoneInfo("America/Chicago")
+    today_midnight = datetime.now(central).replace(hour=0, minute=0, second=0, microsecond=0)
 
+    # start: 5 days ago, at midnight
+    start_date = (today_midnight - timedelta(days=5)).astimezone(timezone.utc)
+    # end: tomorrow, at midnight
+    end_date = (today_midnight + timedelta(days=1)).astimezone(timezone.utc)
 
     # gateSettings contains four callable methods
-    #   void createGateSettings(String officeId, String locationStr, Date startDate, Date end) throws Exception;
-    #   void createGateSettingsGroup(String officeId, String locationStr, Date startDate, Date end, String groupId) throws Exception;
-    #   void createGateSettingsOutlet(String officeId, String locationStr, Date startDate, Date end, String outletId) throws Exception;
-    #   void createGateSettingsOutletFromTs(String officeId, String locationStr, Date startDate, Date end, String outletId, String tsId) throws Exception;
-
-    gateSettings.createGateSettingsOutletFromTs("SWF", "FFLT2",  startCal.getTime(), endCal.getTime(), "Release", "FFLT2.Opening.Const.0.0.Rev-TRWD-Decodes" )
-    gateSettings.createGateSettingsOutletFromTs("SWF", "EAMT2",  startCal.getTime(), endCal.getTime(), "Release", "EAMT2.Opening.Const.0.0.Rev-TRWD-Decodes" )
-    gateSettings.createGateSettingsOutletFromTs("SWF", "TRNT2",  startCal.getTime(), endCal.getTime(), "Release", "TRNT2.Opening.Const.0.0.Rev-TRWD-Decodes" )
-    gateSettings.createGateSettingsOutletFromTs("SWF", "BPRT2",  startCal.getTime(), endCal.getTime(), "Release", "BPRT2.Opening.Const.0.0.Rev-TRWD-Decodes" )
-    gateSettings.createGateSettingsOutletFromTs("SWF", "LLST2",  startCal.getTime(), endCal.getTime(), "Release", "LLST2.Opening.Const.0.0.Rev-BRA-Decodes" )
-    gateSettings.createGateSettingsOutletFromTs("SWF", "GBYT2",  startCal.getTime(), endCal.getTime(), "Release", "GBYT2.Opening.Const.0.0.Rev-BRA-Decodes" )
-    gateSettings.createGateSettingsOutletFromTs("SWF", "PSMT2",  startCal.getTime(), endCal.getTime(), "Release", "PSMT2.Opening.Const.0.0.Rev-BRA-Decodes" )
-    gateSettings.createGateSettingsOutletFromTs("SWF", "MSDT2",  startCal.getTime(), endCal.getTime(), "Release", "MSDT2.Opening.Const.0.0.Rev-LCRA-Decodes" )
-    gateSettings.createGateSettingsOutletFromTs("SWF", "FRHT2",  startCal.getTime(), endCal.getTime(), "Release", "FRHT2.Opening.Const.0.0.Raw-Observer" )
-    gateSettings.createGateSettingsOutletFromTs("SWF", "GPET2",  startCal.getTime(), endCal.getTime(), "Release", "GPET2.Opening.Const.0.0.Raw-Observer" )
+    #   void createGateSettings(String officeId, String locationStr, Instant startDate, Instant end) throws Exception;
+    #   void createGateSettingsGroup(String officeId, String locationStr, Instant startDate, Instant end, String groupId) throws Exception;
+    #   void createGateSettingsOutlet(String officeId, String locationStr, Instant startDate, Instant end, String outletId) throws Exception;
+    #   void createGateSettingsOutletFromTs(String officeId, String locationStr, Instant startDate, Instant end, String outletId, String tsId) throws Exception;
+
+    gateSettings.createGateSettingsOutletFromTs("SWF", "FFLT2",  start_date, end_date, "Release", "FFLT2.Opening.Const.0.0.Rev-TRWD-Decodes" )
+    gateSettings.createGateSettingsOutletFromTs("SWF", "EAMT2",  start_date, end_date, "Release", "EAMT2.Opening.Const.0.0.Rev-TRWD-Decodes" )
+    gateSettings.createGateSettingsOutletFromTs("SWF", "TRNT2",  start_date, end_date, "Release", "TRNT2.Opening.Const.0.0.Rev-TRWD-Decodes" )
+    gateSettings.createGateSettingsOutletFromTs("SWF", "BPRT2",  start_date, end_date, "Release", "BPRT2.Opening.Const.0.0.Rev-TRWD-Decodes" )
+    gateSettings.createGateSettingsOutletFromTs("SWF", "LLST2",  start_date, end_date, "Release", "LLST2.Opening.Const.0.0.Rev-BRA-Decodes" )
+    gateSettings.createGateSettingsOutletFromTs("SWF", "GBYT2",  start_date, end_date, "Release", "GBYT2.Opening.Const.0.0.Rev-BRA-Decodes" )
+    gateSettings.createGateSettingsOutletFromTs("SWF", "PSMT2",  start_date, end_date, "Release", "PSMT2.Opening.Const.0.0.Rev-BRA-Decodes" )
+    gateSettings.createGateSettingsOutletFromTs("SWF", "MSDT2",  start_date, end_date, "Release", "MSDT2.Opening.Const.0.0.Rev-LCRA-Decodes" )
+    gateSettings.createGateSettingsOutletFromTs("SWF", "FRHT2",  start_date, end_date, "Release", "FRHT2.Opening.Const.0.0.Raw-Observer" )
+    gateSettings.createGateSettingsOutletFromTs("SWF", "GPET2",  start_date, end_date, "Release", "GPET2.Opening.Const.0.0.Raw-Observer" )
 
 
 
diff --git a/district-scripts/SWF/InflowCalcComputeEvapAsFlow.py b/district-scripts/SWF/InflowCalcComputeEvapAsFlow.py
index fd6f4e3..6406a79 100644
--- a/district-scripts/SWF/InflowCalcComputeEvapAsFlow.py
+++ b/district-scripts/SWF/InflowCalcComputeEvapAsFlow.py
@@ -2,47 +2,25 @@
 
 
 def run_calculations(registry):
-    # Java imports must happen after regi_session starts the JVM.
-    # the java Calendar class is used to create java Date objects
-    from java.util import Calendar
-    from java.util import TimeZone
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
 
 
     # this gets a ScriptableInflow instance.
     inflowCalc = registry.getCalculation(1.0, "Inflow")
 
-    # configure the start calendar
-    ##startCal = Calendar.getInstance(TimeZone.getTimeZone('US/Central'))
-    ##
-    ##
-    ##startCal.clear()
-    ##startCal.set(Calendar.YEAR, 2018)
-    ##startCal.set(Calendar.MONTH, 11)
-    ##
-    ##endCal = Calendar.getInstance(TimeZone.getTimeZone('US/Central'))
-    ##endCal.clear()
-    ##endCal.set(Calendar.YEAR, 2019)
-    ##endCal.set(Calendar.MONTH, 0)
-    ##endCal.set(Calendar.DAY_OF_MONTH, 7)
-
-    startCal = Calendar.getInstance(TimeZone.getTimeZone('US/Central'))
-    # startCal.clear()
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    startCal.set(Calendar.HOUR_OF_DAY, 0)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-    # startCal.set(Calendar.YEAR, 2015)
-    # startCal.set(Calendar.MONTH, 9)
-
-    # create a java Calendar object that will be used to create the end Date
-    endCal = Calendar.getInstance(TimeZone.getTimeZone('US/Central'))
-    # endCal.clear()
-    endCal.add(Calendar.DAY_OF_MONTH, 1)
-    endCal.set(Calendar.HOUR_OF_DAY, 0)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
+    # configure the start/end dates
+    ##central = ZoneInfo("America/Chicago")
+    ##start_date = (datetime(2018, 12, 1, tzinfo=central)).astimezone(timezone.utc)
+    ##end_date = (datetime(2019, 1, 7, tzinfo=central)).astimezone(timezone.utc)
+
+    central = ZoneInfo("America/Chicago")
+    today_midnight = datetime.now(central).replace(hour=0, minute=0, second=0, microsecond=0)
+
+    # start: 5 days ago, at midnight
+    start_date = (today_midnight - timedelta(days=5)).astimezone(timezone.utc)
+    # end: tomorrow, at midnight
+    end_date = (today_midnight + timedelta(days=1)).astimezone(timezone.utc)
 
     locationList = ["WTYT2","JSPT2","TBLT2","SCLT2","TXKT2","BSLT2","JFNT2","CLDL1",
                     "BPRT2","EAMT2","FLWT2","BNBT2","JPLT2","GPET2","RRLT2","LEWT2",
@@ -51,7 +29,7 @@ def run_calculations(registry):
                     "SOMT2","LLST2","TBRT2","SAGT2","HORT2","MSDT2","SMCT2"]
 
     for loc in locationList:
-        inflowCalc.computeEvapAsFlow("SWF", loc,  startCal.getTime(), endCal.getTime())
+        inflowCalc.computeEvapAsFlow("SWF", loc,  start_date, end_date)
 
 
 if __name__ == "__main__":
diff --git a/district-scripts/SWF/InflowCalcComputedInflow.py b/district-scripts/SWF/InflowCalcComputedInflow.py
index 99d5331..cf8e019 100644
--- a/district-scripts/SWF/InflowCalcComputedInflow.py
+++ b/district-scripts/SWF/InflowCalcComputedInflow.py
@@ -2,42 +2,28 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    # the java Calendar class is used to create java Date objects
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless.calculator.inflow import InflowComputationStorageOption
 
+
     # this gets a ScriptableInflow instance.
     inflowCalc = registry.getCalculation(1.0, "Inflow")
 
-    # configure the start calendar
-    ##startCal = Calendar.getInstance(TimeZone.getTimeZone('US/Central'))
-    ##
-    ##
-    ##startCal.clear()
-    ##startCal.set(Calendar.YEAR, 2019)
-    ##startCal.set(Calendar.MONTH, 1)
-    ##
-    ##endCal = Calendar.getInstance(TimeZone.getTimeZone('US/Central'))
-    ##endCal.clear()
-    ##endCal.set(Calendar.YEAR, 2019)
-    ##endCal.set(Calendar.MONTH, 1)
-    ##endCal.set(Calendar.DAY_OF_MONTH, 4)
+    # configure the start/end dates
+    ##central = ZoneInfo("America/Chicago")
+    ##start_date = (datetime(2019, 2, 1, tzinfo=central)).astimezone(timezone.utc)
+    ##end_date = (datetime(2019, 2, 4, tzinfo=central)).astimezone(timezone.utc)
+
+    central = ZoneInfo("America/Chicago")
+    today_midnight = datetime.now(central).replace(hour=0, minute=0, second=0, microsecond=0)
 
-    startCal = Calendar.getInstance(TimeZone.getTimeZone('US/Central'))
-    startCal.add(Calendar.DAY_OF_MONTH, -4)
-    startCal.set(Calendar.HOUR, 0)        ######use Calendar.HOUR_OF_DAY
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-    # create a java Calendar object that will be used to create the end Date
-    endCal = Calendar.getInstance(TimeZone.getTimeZone('US/Central'))
-    endCal.add(Calendar.DAY_OF_MONTH, 1)
-    endCal.set(Calendar.HOUR, 0)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
+    # start: 4 days ago, at midnight
+    start_date = (today_midnight - timedelta(days=4)).astimezone(timezone.utc)
+    # end: tomorrow, at midnight
+    end_date = (today_midnight + timedelta(days=1)).astimezone(timezone.utc)
 
     # inflowCalc includes a setComputationStorageOptions function, which takes in either one or many
     # InflowComputationStorageOption values.  This is used by computeInflow to determine if it should save additional
@@ -66,7 +52,7 @@ def run_calculations(registry):
                     "GBYT2","ALAT2","ACTT2","PCTT2","BLNT2","STIT2","GGLT2","GNGT2",
                     "SOMT2","LLST2","TBRT2","SAGT2","HORT2","SMCT2","MSDT2"]
     for loc in locationList:
-        inflowCalc.computeInflow("SWF", loc, startCal.getTime(), endCal.getTime())
+        inflowCalc.computeInflow("SWF", loc, start_date, end_date)
 
 
 if __name__ == "__main__":
diff --git a/district-scripts/SWL/Big3-GateFlow.py b/district-scripts/SWL/Big3-GateFlow.py
index 3b09287..b4b1eb3 100644
--- a/district-scripts/SWL/Big3-GateFlow.py
+++ b/district-scripts/SWL/Big3-GateFlow.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,31 +67,15 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
-    # the gate flow calculations requires a start and end time.
-    # here we create a java Calendar object that will be used to create the start Date
-    startCal = Calendar.getInstance(timeZone)
-    # startCal.clear()
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    startCal.set(Calendar.HOUR_OF_DAY, 0)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    # startCal.set(Calendar.YEAR, 2015)
-    # startCal.set(Calendar.MONTH, 9)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-    # create a java Calendar object that will be used to create the end Date
-    endCal = Calendar.getInstance(timeZone)
-    # endCal.clear()
-    ##################endCal.add(Calendar.DAY_OF_MONTH, 5)
-    endCal.add(Calendar.DAY_OF_MONTH, 1)
-    endCal.set(Calendar.HOUR_OF_DAY, 0)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    # endCal.set(Calendar.YEAR, 2015)
-    # endCal.set(Calendar.MONTH, 11)
-    endCal.set(Calendar.MILLISECOND, 0)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    today_midnight = datetime.now(central).replace(hour=0, minute=0, second=0, microsecond=0)
+
+    # start: 5 days ago, at midnight
+    start_date = (today_midnight - timedelta(days=5)).astimezone(timezone.utc)
+    # end: tomorrow, at midnight
+    end_date = (today_midnight + timedelta(days=1)).astimezone(timezone.utc)
 
     officeID = "SWL"
 
@@ -99,7 +85,7 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
     # By setting the following parameter to True, the following flow groups in the list FlowGroupList will all be calculated. Items can be commented out
     # or commented back in individually. To turn this option off, set the following parameter to False. User can determine which flow group they want to calculate
     # by changing the "flowGroup" variable.
@@ -128,12 +114,12 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     if calculateSingleFlowGroups:
         for location in locationList:
             print("Now Running", location, "SINGLE")
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup)
 
     if calculateAllFlowGroups:
         for location in FlowGroupList:
             print("Now Running", location, "GROUP")
-            compute_All_Flowgroups(officeID, location, startCal, endCal)
+            compute_All_Flowgroups(officeID, location, start_date, end_date)
 
 
 
diff --git a/district-scripts/SWL/Big3-InflowCalcMultipleActions.py b/district-scripts/SWL/Big3-InflowCalcMultipleActions.py
index 04861a9..bdd7161 100644
--- a/district-scripts/SWL/Big3-InflowCalcMultipleActions.py
+++ b/district-scripts/SWL/Big3-InflowCalcMultipleActions.py
@@ -2,12 +2,13 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    # the java Calendar class is used to create java Date objects
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
+
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -43,31 +44,16 @@ def run_calculations(registry):
     # this gets a scriptable Pool Percent object
     inflowCalc = registry.getCalculation(1.0, "Inflow")
 
-    # configure the start calendar'
-    #startCal = Calendar.getInstance(TimeZone.getTimeZone('US/Central'))
-    timeZone = TimeZone.getTimeZone("US/Central")
-
-    #startCal.clear()
-    #startCal.set(Calendar.YEAR, 2015)
-    #startCal.set(Calendar.MONTH, 4)
-
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -7)
-    startCal.set(Calendar.HOUR_OF_DAY, 0)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-    endCal = Calendar.getInstance(timeZone)
-    endCal.add(Calendar.DAY_OF_MONTH, 1)
-    endCal.set(Calendar.HOUR_OF_DAY, 0)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    today_midnight = datetime.now(central).replace(hour=0, minute=0, second=0, microsecond=0)
 
     officeID = "SWL"
-    startDate = startCal.getTime()
-    endDate = endCal.getTime()
+    # start: 7 days ago, at midnight
+    startDate = (today_midnight - timedelta(days=7)).astimezone(timezone.utc)
+    # end: tomorrow, at midnight
+    endDate = (today_midnight + timedelta(days=1)).astimezone(timezone.utc)
 
     # inflowCalc contains 4 callable methods:
     # autoAdjust
diff --git a/district-scripts/SWL/Millwd-Tri-Lks-GateFlow.py b/district-scripts/SWL/Millwd-Tri-Lks-GateFlow.py
index 998bddc..e0a90f6 100644
--- a/district-scripts/SWL/Millwd-Tri-Lks-GateFlow.py
+++ b/district-scripts/SWL/Millwd-Tri-Lks-GateFlow.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,31 +67,15 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
-    # the gate flow calculations requires a start and end time.
-    # here we create a java Calendar object that will be used to create the start Date
-    startCal = Calendar.getInstance(timeZone)
-    # startCal.clear()
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    startCal.set(Calendar.HOUR_OF_DAY, 0)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    # startCal.set(Calendar.YEAR, 2015)
-    # startCal.set(Calendar.MONTH, 9)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-    # create a java Calendar object that will be used to create the end Date
-    endCal = Calendar.getInstance(timeZone)
-    # endCal.clear()
-    ##################endCal.add(Calendar.DAY_OF_MONTH, 5)
-    endCal.add(Calendar.DAY_OF_MONTH, 1)
-    endCal.set(Calendar.HOUR_OF_DAY, 0)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    # endCal.set(Calendar.YEAR, 2015)
-    # endCal.set(Calendar.MONTH, 11)
-    endCal.set(Calendar.MILLISECOND, 0)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    today_midnight = datetime.now(central).replace(hour=0, minute=0, second=0, microsecond=0)
+
+    # start: 5 days ago, at midnight
+    start_date = (today_midnight - timedelta(days=5)).astimezone(timezone.utc)
+    # end: tomorrow, at midnight
+    end_date = (today_midnight + timedelta(days=1)).astimezone(timezone.utc)
 
     officeID = "SWL"
 
@@ -99,7 +85,7 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
     # By setting the following parameter to True, the following flow groups in the list FlowGroupList will all be calculated. Items can be commented out
     # or commented back in individually. To turn this option off, set the following parameter to False. User can determine which flow group they want to calculate
     # by changing the "flowGroup" variable.
@@ -129,12 +115,12 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     if calculateSingleFlowGroups:
         for location in locationList:
             print("Now Running", location, "SINGLE")
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup)
 
     if calculateAllFlowGroups:
         for location in FlowGroupList:
             print("Now Running", location, "GROUP")
-            compute_All_Flowgroups(officeID, location, startCal, endCal)
+            compute_All_Flowgroups(officeID, location, start_date, end_date)
 
 
 
diff --git a/district-scripts/SWL/Millwd-Tri-Lks-InflowCalcMultipleActions.py b/district-scripts/SWL/Millwd-Tri-Lks-InflowCalcMultipleActions.py
index fc8a71b..c682ce8 100644
--- a/district-scripts/SWL/Millwd-Tri-Lks-InflowCalcMultipleActions.py
+++ b/district-scripts/SWL/Millwd-Tri-Lks-InflowCalcMultipleActions.py
@@ -2,12 +2,13 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    # the java Calendar class is used to create java Date objects
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
+
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -43,31 +44,16 @@ def run_calculations(registry):
     # this gets a scriptable Pool Percent object
     inflowCalc = registry.getCalculation(1.0, "Inflow")
 
-    # configure the start calendar'
-    #startCal = Calendar.getInstance(TimeZone.getTimeZone('US/Central'))
-    timeZone = TimeZone.getTimeZone("US/Central")
-
-    #startCal.clear()
-    #startCal.set(Calendar.YEAR, 2015)
-    #startCal.set(Calendar.MONTH, 4)
-
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -7)
-    startCal.set(Calendar.HOUR_OF_DAY, 0)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-    endCal = Calendar.getInstance(timeZone)
-    endCal.add(Calendar.DAY_OF_MONTH, 1)
-    endCal.set(Calendar.HOUR_OF_DAY, 0)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    today_midnight = datetime.now(central).replace(hour=0, minute=0, second=0, microsecond=0)
 
     officeID = "SWL"
-    startDate = startCal.getTime()
-    endDate = endCal.getTime()
+    # start: 7 days ago, at midnight
+    startDate = (today_midnight - timedelta(days=7)).astimezone(timezone.utc)
+    # end: tomorrow, at midnight
+    endDate = (today_midnight + timedelta(days=1)).astimezone(timezone.utc)
 
     # inflowCalc contains 4 callable methods:
     # autoAdjust
diff --git a/district-scripts/SWL/WhiteR-GateFlow.py b/district-scripts/SWL/WhiteR-GateFlow.py
index 270a0f4..c620f43 100644
--- a/district-scripts/SWL/WhiteR-GateFlow.py
+++ b/district-scripts/SWL/WhiteR-GateFlow.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,32 +67,15 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
-    # the gate flow calculations requires a start and end time.
-    # here we create a java Calendar object that will be used to create the start Date
-    startCal = Calendar.getInstance(timeZone)
-    # startCal.clear()
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    startCal.set(Calendar.HOUR_OF_DAY, 0)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    # startCal.set(Calendar.YEAR, 2015)
-    # startCal.set(Calendar.MONTH, 9)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-    # create a java Calendar object that will be used to create the end Date
-    endCal = Calendar.getInstance(timeZone)
-    # endCal.clear()
-    ##################endCal.add(Calendar.DAY_OF_MONTH, 5)
-    #endCal.add(Calendar.DAY_OF_MONTH, 1)
-    endCal.add(Calendar.DAY_OF_MONTH, 1)
-    endCal.set(Calendar.HOUR_OF_DAY, 0)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    # endCal.set(Calendar.YEAR, 2015)
-    # endCal.set(Calendar.MONTH, 11)
-    endCal.set(Calendar.MILLISECOND, 0)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    today_midnight = datetime.now(central).replace(hour=0, minute=0, second=0, microsecond=0)
+
+    # start: 5 days ago, at midnight
+    start_date = (today_midnight - timedelta(days=5)).astimezone(timezone.utc)
+    # end: tomorrow, at midnight
+    end_date = (today_midnight + timedelta(days=1)).astimezone(timezone.utc)
 
     officeID = "SWL"
 
@@ -100,7 +85,7 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
     # By setting the following parameter to True, the following flow groups in the list FlowGroupList will all be calculated. Items can be commented out
     # or commented back in individually. To turn this option off, set the following parameter to False. User can determine which flow group they want to calculate
     # by changing the "flowGroup" variable.
@@ -131,12 +116,12 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     if calculateSingleFlowGroups:
         for location in locationList:
             print("Now Running", location, "SINGLE")
-            compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup)
+            compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup)
 
     if calculateAllFlowGroups:
         for location in FlowGroupList:
             print("Now Running", location, "GROUP")
-            compute_All_Flowgroups(officeID, location, startCal, endCal)
+            compute_All_Flowgroups(officeID, location, start_date, end_date)
 
 
 
diff --git a/district-scripts/SWL/WhiteR-InflowCalcMultipleActions.py b/district-scripts/SWL/WhiteR-InflowCalcMultipleActions.py
index 9b548c0..0765106 100644
--- a/district-scripts/SWL/WhiteR-InflowCalcMultipleActions.py
+++ b/district-scripts/SWL/WhiteR-InflowCalcMultipleActions.py
@@ -2,12 +2,13 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    # the java Calendar class is used to create java Date objects
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
+
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -43,31 +44,16 @@ def run_calculations(registry):
     # this gets a scriptable Pool Percent object
     inflowCalc = registry.getCalculation(1.0, "Inflow")
 
-    # configure the start calendar'
-    #startCal = Calendar.getInstance(TimeZone.getTimeZone('US/Central'))
-    timeZone = TimeZone.getTimeZone("US/Central")
-
-    #startCal.clear()
-    #startCal.set(Calendar.YEAR, 2015)
-    #startCal.set(Calendar.MONTH, 4)
-
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -7)
-    startCal.set(Calendar.HOUR_OF_DAY, 0)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-    endCal = Calendar.getInstance(timeZone)
-    endCal.add(Calendar.DAY_OF_MONTH, 1)
-    endCal.set(Calendar.HOUR_OF_DAY, 0)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    today_midnight = datetime.now(central).replace(hour=0, minute=0, second=0, microsecond=0)
 
     officeID = "SWL"
-    startDate = startCal.getTime()
-    endDate = endCal.getTime()
+    # start: 7 days ago, at midnight
+    startDate = (today_midnight - timedelta(days=7)).astimezone(timezone.utc)
+    # end: tomorrow, at midnight
+    endDate = (today_midnight + timedelta(days=1)).astimezone(timezone.utc)
 
     # inflowCalc contains 4 callable methods:
     # autoAdjust
diff --git a/district-scripts/SWT/GateFlowGroup1.py b/district-scripts/SWT/GateFlowGroup1.py
index 9018dc7..c9d0cb3 100644
--- a/district-scripts/SWT/GateFlowGroup1.py
+++ b/district-scripts/SWT/GateFlowGroup1.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,31 +67,22 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
 
     # Defaults to start of the day 5 days ago, and ends at the top of the current hour today
-    # configure the start calendar
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    #startCal.add(Calendar.HOUR, -7)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-
-    # configure the end calendar
-    endCal = Calendar.getInstance(timeZone)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    #endCal.add(Calendar.MONTH, -3)
-
-    # Calendar can be adjusted using the following functions:
-    #   startCal.set(Calendar.DATE, 1)          # Sets the date of the calendar.
-    #   startCal.set(Calendar.HOUR_OF_DAY, 1)   # Sets the hour of the day to 0100 (1-24)
-    #   startCal.set(Calendar.YEAR, 2020)       # Sets the year
-    #   startCal.set(Calendar.MONTH, 4)         # Sets the month (month 4 means May to Java)
+    end_date_dt = datetime.now(central).replace(minute=0, second=0, microsecond=0)
+    start_date_dt = end_date_dt - timedelta(days=5)
+    #start_date_dt = end_date_dt - timedelta(days=5, hours=7)
+
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
+
+    # Dates can be adjusted using normal datetime arithmetic/replace, e.g.:
+    #   start_date_dt = start_date_dt.replace(day=1)                  # start of month
+    #   start_date_dt = start_date_dt.replace(hour=1)                 # 0100 local time
+    #   start_date_dt = start_date_dt.replace(year=2020, month=5)     # month is 1-indexed here
 
     officeID = "SWT"
 
@@ -99,52 +92,52 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
 
     #
     #  GROUP 1 PROJECTS (SELF-TIMED TRANSMISSIONS WITHIN THE FIRST 2 MINUTES OF THE TOP OF THE HOUR)
     #
 
     #FOSS
-    gateCalc.computeFlowGroup("SWT", "FOSS",  startCal.getTime(), endCal.getTime(), "Flow.FOSS.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "FOSS",  startCal.getTime(), endCal.getTime(), "Flow.FOSS.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "FOSS",  start_date, end_date, "Flow.FOSS.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "FOSS",  start_date, end_date, "Flow.FOSS.Gated_Total")
 
     #FCOB
-    gateCalc.computeFlowGroup("SWT", "FCOB",  startCal.getTime(), endCal.getTime(), "Flow.FCOB.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "FCOB",  startCal.getTime(), endCal.getTime(), "Flow.FCOB.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "FCOB",  start_date, end_date, "Flow.FCOB.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "FCOB",  start_date, end_date, "Flow.FCOB.Gated_Total")
 
     #SKIA
-    gateCalc.computeFlowGroup("SWT", "SKIA",  startCal.getTime(), endCal.getTime(), "Flow.SKIA.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "SKIA",  startCal.getTime(), endCal.getTime(), "Flow.SKIA.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "SKIA",  start_date, end_date, "Flow.SKIA.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "SKIA",  start_date, end_date, "Flow.SKIA.Gated_Total")
 
     #HEYB
-    gateCalc.computeFlowGroup("SWT", "HEYB",  startCal.getTime(), endCal.getTime(), "Flow.HEYB.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "HEYB",  startCal.getTime(), endCal.getTime(), "Flow.HEYB.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "HEYB",  start_date, end_date, "Flow.HEYB.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "HEYB",  start_date, end_date, "Flow.HEYB.Gated_Total")
 
     #KAWL
-    gateCalc.computeFlowGroup("SWT", "KAWL",  startCal.getTime(), endCal.getTime(), "Flow.KAWL.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "KAWL",  startCal.getTime(), endCal.getTime(), "Flow.KAWL.Gated_Total")
-    gateCalc.computeFlowGroup("SWT", "KAWL",  startCal.getTime(), endCal.getTime(), "Flow.KAWL.Turbine_Total") 
+    gateCalc.computeFlowGroup("SWT", "KAWL",  start_date, end_date, "Flow.KAWL.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "KAWL",  start_date, end_date, "Flow.KAWL.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "KAWL",  start_date, end_date, "Flow.KAWL.Turbine_Total") 
 
     #OOLO
-    gateCalc.computeFlowGroup("SWT", "OOLO",  startCal.getTime(), endCal.getTime(), "Flow.OOLO.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "OOLO",  startCal.getTime(), endCal.getTime(), "Flow.OOLO.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "OOLO",  start_date, end_date, "Flow.OOLO.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "OOLO",  start_date, end_date, "Flow.OOLO.Gated_Total")
 
     #COPA
-    gateCalc.computeFlowGroup("SWT", "COPA",  startCal.getTime(), endCal.getTime(), "Flow.COPA.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "COPA",  startCal.getTime(), endCal.getTime(), "Flow.COPA.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "COPA",  start_date, end_date, "Flow.COPA.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "COPA",  start_date, end_date, "Flow.COPA.Gated_Total")
 
     #HULA
-    gateCalc.computeFlowGroup("SWT", "HULA",  startCal.getTime(), endCal.getTime(), "Flow.HULA.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "HULA",  startCal.getTime(), endCal.getTime(), "Flow.HULA.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "HULA",  start_date, end_date, "Flow.HULA.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "HULA",  start_date, end_date, "Flow.HULA.Gated_Total")
 
     #ELKC
-    gateCalc.computeFlowGroup("SWT", "ELKC",  startCal.getTime(), endCal.getTime(), "Flow.ELKC.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "ELKC",  startCal.getTime(), endCal.getTime(), "Flow.ELKC.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "ELKC",  start_date, end_date, "Flow.ELKC.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "ELKC",  start_date, end_date, "Flow.ELKC.Gated_Total")
 
     #FALL
-    gateCalc.computeFlowGroup("SWT", "FALL",  startCal.getTime(), endCal.getTime(), "Flow.FALL.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "FALL",  startCal.getTime(), endCal.getTime(), "Flow.FALL.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "FALL",  start_date, end_date, "Flow.FALL.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "FALL",  start_date, end_date, "Flow.FALL.Gated_Total")
 
 
 
diff --git a/district-scripts/SWT/GateFlowGroup2.py b/district-scripts/SWT/GateFlowGroup2.py
index 8beac17..d75c4fb 100644
--- a/district-scripts/SWT/GateFlowGroup2.py
+++ b/district-scripts/SWT/GateFlowGroup2.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,31 +67,22 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
 
     # Defaults to start of the day 5 days ago, and ends at the top of the current hour today
-    # configure the start calendar
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    #startCal.add(Calendar.HOUR, -7)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-
-    # configure the end calendar
-    endCal = Calendar.getInstance(timeZone)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    #endCal.add(Calendar.MONTH, -3)
-
-    # Calendar can be adjusted using the following functions:
-    #   startCal.set(Calendar.DATE, 1)          # Sets the date of the calendar.
-    #   startCal.set(Calendar.HOUR_OF_DAY, 1)   # Sets the hour of the day to 0100 (1-24)
-    #   startCal.set(Calendar.YEAR, 2020)       # Sets the year
-    #   startCal.set(Calendar.MONTH, 4)         # Sets the month (month 4 means May to Java)
+    end_date_dt = datetime.now(central).replace(minute=0, second=0, microsecond=0)
+    start_date_dt = end_date_dt - timedelta(days=5)
+    #start_date_dt = end_date_dt - timedelta(days=5, hours=7)
+
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
+
+    # Dates can be adjusted using normal datetime arithmetic/replace, e.g.:
+    #   start_date_dt = start_date_dt.replace(day=1)                  # start of month
+    #   start_date_dt = start_date_dt.replace(hour=1)                 # 0100 local time
+    #   start_date_dt = start_date_dt.replace(year=2020, month=5)     # month is 1-indexed here
 
     officeID = "SWT"
 
@@ -99,32 +92,32 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
 
     #
     #  GROUP 2 PROJECTS (SELF-TIMED TRANSMISSIONS WITHIN THE FIRST 2 - 4 MINUTES OF THE TOP OF THE HOUR)
     #
 
     #ARCA
-    gateCalc.computeFlowGroup("SWT", "ARCA",  startCal.getTime(), endCal.getTime(), "Flow.ARCA.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "ARCA",  startCal.getTime(), endCal.getTime(), "Flow.ARCA.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "ARCA",  start_date, end_date, "Flow.ARCA.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "ARCA",  start_date, end_date, "Flow.ARCA.Gated_Total")
 
     #ARBU
-    gateCalc.computeFlowGroup("SWT", "ARBU",  startCal.getTime(), endCal.getTime(), "Flow.ARBU.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "ARBU",  startCal.getTime(), endCal.getTime(), "Flow.ARBU.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "ARBU",  start_date, end_date, "Flow.ARBU.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "ARBU",  start_date, end_date, "Flow.ARBU.Gated_Total")
 
     #BIRC
-    gateCalc.computeFlowGroup("SWT", "BIRC",  startCal.getTime(), endCal.getTime(), "Flow.BIRC.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "BIRC",  startCal.getTime(), endCal.getTime(), "Flow.BIRC.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "BIRC",  start_date, end_date, "Flow.BIRC.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "BIRC",  start_date, end_date, "Flow.BIRC.Gated_Total")
 
     #ROBE
-    gateCalc.computeFlowGroup("SWT", "ROBE",  startCal.getTime(), endCal.getTime(), "Flow.ROBE.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "ROBE",  startCal.getTime(), endCal.getTime(), "Flow.ROBE.Gated_Total")
-    gateCalc.computeFlowGroup("SWT", "ROBE",  startCal.getTime(), endCal.getTime(), "Flow.ROBE.Turbine_Total")
+    gateCalc.computeFlowGroup("SWT", "ROBE",  start_date, end_date, "Flow.ROBE.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "ROBE",  start_date, end_date, "Flow.ROBE.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "ROBE",  start_date, end_date, "Flow.ROBE.Turbine_Total")
 
     #WAUR
-    gateCalc.computeFlowGroup("SWT", "WAUR",  startCal.getTime(), endCal.getTime(), "Flow.WAUR.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "WAUR",  startCal.getTime(), endCal.getTime(), "Flow.WAUR.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "WAUR",  start_date, end_date, "Flow.WAUR.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "WAUR",  start_date, end_date, "Flow.WAUR.Gated_Total")
 
 
 
diff --git a/district-scripts/SWT/GateFlowGroup3.py b/district-scripts/SWT/GateFlowGroup3.py
index cf5a667..28a3b9b 100644
--- a/district-scripts/SWT/GateFlowGroup3.py
+++ b/district-scripts/SWT/GateFlowGroup3.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,31 +67,23 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
 
     # Defaults to start of the day 5 days ago, and ends at the top of the current hour today
-    # configure the start calendar
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    #startCal.add(Calendar.HOUR, -7)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-
-    # configure the end calendar
-    endCal = Calendar.getInstance(timeZone)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    #endCal.add(Calendar.DAY_OF_MONTH, -12)
-
-    # Calendar can be adjusted using the following functions:
-    #   startCal.set(Calendar.DATE, 1)          # Sets the date of the calendar.
-    #   startCal.set(Calendar.HOUR_OF_DAY, 1)   # Sets the hour of the day to 0100 (1-24)
-    #   startCal.set(Calendar.YEAR, 2020)       # Sets the year
-    #   startCal.set(Calendar.MONTH, 4)         # Sets the month (month 4 means May to Java)
+    end_date_dt = datetime.now(central).replace(minute=0, second=0, microsecond=0)
+    start_date_dt = end_date_dt - timedelta(days=5)
+    #start_date_dt = end_date_dt - timedelta(days=5, hours=7)
+    #end_date_dt = end_date_dt - timedelta(days=12)
+
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
+
+    # Dates can be adjusted using normal datetime arithmetic/replace, e.g.:
+    #   start_date_dt = start_date_dt.replace(day=1)                  # start of month
+    #   start_date_dt = start_date_dt.replace(hour=1)                 # 0100 local time
+    #   start_date_dt = start_date_dt.replace(year=2020, month=5)     # month is 1-indexed here
 
     officeID = "SWT"
 
@@ -99,40 +93,40 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
 
     #
     #  GROUP 3 PROJECTS (SELF-TIMED TRANSMISSIONS WITHIN 5 TO 8 MINUTES OF THE TOP OF THE HOUR)
     #
 
     #COUN
-    gateCalc.computeFlowGroup("SWT", "COUN",  startCal.getTime(), endCal.getTime(), "Flow.COUN.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "COUN",  startCal.getTime(), endCal.getTime(), "Flow.COUN.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "COUN",  start_date, end_date, "Flow.COUN.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "COUN",  start_date, end_date, "Flow.COUN.Gated_Total")
 
     #HUGO
-    gateCalc.computeFlowGroup("SWT", "HUGO",  startCal.getTime(), endCal.getTime(), "Flow.HUGO.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "HUGO",  startCal.getTime(), endCal.getTime(), "Flow.HUGO.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "HUGO",  start_date, end_date, "Flow.HUGO.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "HUGO",  start_date, end_date, "Flow.HUGO.Gated_Total")
 
     #MARI
-    gateCalc.computeFlowGroup("SWT", "MARI",  startCal.getTime(), endCal.getTime(), "Flow.MARI.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "MARI",  startCal.getTime(), endCal.getTime(), "Flow.MARI.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "MARI",  start_date, end_date, "Flow.MARI.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "MARI",  start_date, end_date, "Flow.MARI.Gated_Total")
 
     #PATM
-    gateCalc.computeFlowGroup("SWT", "PATM",  startCal.getTime(), endCal.getTime(), "Flow.PATM.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "PATM",  startCal.getTime(), endCal.getTime(), "Flow.PATM.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "PATM",  start_date, end_date, "Flow.PATM.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "PATM",  start_date, end_date, "Flow.PATM.Gated_Total")
 
     #FSUP
-    gateCalc.computeFlowGroup("SWT", "FSUP",  startCal.getTime(), endCal.getTime(), "Flow.FSUP.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "FSUP",  startCal.getTime(), endCal.getTime(), "Flow.FSUP.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "FSUP",  start_date, end_date, "Flow.FSUP.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "FSUP",  start_date, end_date, "Flow.FSUP.Gated_Total")
 
     #CANT
-    gateCalc.computeFlowGroup("SWT", "CANT",  startCal.getTime(), endCal.getTime(), "Flow.CANT.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "CANT",  startCal.getTime(), endCal.getTime(), "Flow.CANT.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "CANT",  start_date, end_date, "Flow.CANT.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "CANT",  start_date, end_date, "Flow.CANT.Gated_Total")
 
     #HUDS
-    gateCalc.computeFlowGroup("SWT", "HUDS",  startCal.getTime(), endCal.getTime(), "Flow.HUDS.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "HUDS",  startCal.getTime(), endCal.getTime(), "Flow.HUDS.Turbine_Total")
-    gateCalc.computeFlowGroup("SWT", "HUDS",  startCal.getTime(), endCal.getTime(), "Flow.HUDS.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "HUDS",  start_date, end_date, "Flow.HUDS.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "HUDS",  start_date, end_date, "Flow.HUDS.Turbine_Total")
+    gateCalc.computeFlowGroup("SWT", "HUDS",  start_date, end_date, "Flow.HUDS.Gated_Total")
 
 
 
diff --git a/district-scripts/SWT/GateFlowGroup4.py b/district-scripts/SWT/GateFlowGroup4.py
index c42c619..5ce4412 100644
--- a/district-scripts/SWT/GateFlowGroup4.py
+++ b/district-scripts/SWT/GateFlowGroup4.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,31 +67,22 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
 
     # Defaults to start of the day 5 days ago, and ends at the top of the current hour today
-    # configure the start calendar
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    #startCal.add(Calendar.HOUR, -7)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-
-    # configure the end calendar
-    endCal = Calendar.getInstance(timeZone)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    #endCal.add(Calendar.MONTH, -3)
-
-    # Calendar can be adjusted using the following functions:
-    #   startCal.set(Calendar.DATE, 1)          # Sets the date of the calendar.
-    #   startCal.set(Calendar.HOUR_OF_DAY, 1)   # Sets the hour of the day to 0100 (1-24)
-    #   startCal.set(Calendar.YEAR, 2020)       # Sets the year
-    #   startCal.set(Calendar.MONTH, 4)         # Sets the month (month 4 means May to Java)
+    end_date_dt = datetime.now(central).replace(minute=0, second=0, microsecond=0)
+    start_date_dt = end_date_dt - timedelta(days=5)
+    #start_date_dt = end_date_dt - timedelta(days=5, hours=7)
+
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
+
+    # Dates can be adjusted using normal datetime arithmetic/replace, e.g.:
+    #   start_date_dt = start_date_dt.replace(day=1)                  # start of month
+    #   start_date_dt = start_date_dt.replace(hour=1)                 # 0100 local time
+    #   start_date_dt = start_date_dt.replace(year=2020, month=5)     # month is 1-indexed here
 
     officeID = "SWT"
 
@@ -99,7 +92,7 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
 
 
     #
@@ -107,27 +100,27 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     #
 
     #DENI
-    gateCalc.computeFlowGroup("SWT", "DENI",  startCal.getTime(), endCal.getTime(), "Flow.DENI.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "DENI",  startCal.getTime(), endCal.getTime(), "Flow.DENI.Turbine_Total")
-    gateCalc.computeFlowGroup("SWT", "DENI",  startCal.getTime(), endCal.getTime(), "Flow.DENI.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "DENI",  start_date, end_date, "Flow.DENI.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "DENI",  start_date, end_date, "Flow.DENI.Turbine_Total")
+    gateCalc.computeFlowGroup("SWT", "DENI",  start_date, end_date, "Flow.DENI.Gated_Total")
 
     #PINE
-    gateCalc.computeFlowGroup("SWT", "PINE",  startCal.getTime(), endCal.getTime(), "Flow.PINE.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "PINE",  startCal.getTime(), endCal.getTime(), "Flow.PINE.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "PINE",  start_date, end_date, "Flow.PINE.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "PINE",  start_date, end_date, "Flow.PINE.Gated_Total")
 
     #BROK
-    gateCalc.computeFlowGroup("SWT", "BROK",  startCal.getTime(), endCal.getTime(), "Flow.BROK.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "BROK",  startCal.getTime(), endCal.getTime(), "Flow.BROK.Turbine_Total")
-    gateCalc.computeFlowGroup("SWT", "BROK",  startCal.getTime(), endCal.getTime(), "Flow.BROK.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "BROK",  start_date, end_date, "Flow.BROK.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "BROK",  start_date, end_date, "Flow.BROK.Turbine_Total")
+    gateCalc.computeFlowGroup("SWT", "BROK",  start_date, end_date, "Flow.BROK.Gated_Total")
 
     #SARD
-    gateCalc.computeFlowGroup("SWT", "SARD",  startCal.getTime(), endCal.getTime(), "Flow.SARD.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "SARD",  startCal.getTime(), endCal.getTime(), "Flow.SARD.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "SARD",  start_date, end_date, "Flow.SARD.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "SARD",  start_date, end_date, "Flow.SARD.Gated_Total")
 
     #EUFA
-    gateCalc.computeFlowGroup("SWT", "EUFA",  startCal.getTime(), endCal.getTime(), "Flow.EUFA.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "EUFA",  startCal.getTime(), endCal.getTime(), "Flow.EUFA.Turbine_Total")
-    gateCalc.computeFlowGroup("SWT", "EUFA",  startCal.getTime(), endCal.getTime(), "Flow.EUFA.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "EUFA",  start_date, end_date, "Flow.EUFA.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "EUFA",  start_date, end_date, "Flow.EUFA.Turbine_Total")
+    gateCalc.computeFlowGroup("SWT", "EUFA",  start_date, end_date, "Flow.EUFA.Gated_Total")
 
 
 
diff --git a/district-scripts/SWT/GateFlowGroup5.py b/district-scripts/SWT/GateFlowGroup5.py
index f0133ba..2401e09 100644
--- a/district-scripts/SWT/GateFlowGroup5.py
+++ b/district-scripts/SWT/GateFlowGroup5.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,31 +67,22 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
 
     # Defaults to start of the day 5 days ago, and ends at the top of the current hour today
-    # configure the start calendar
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    #startCal.add(Calendar.HOUR, -7)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-
-    # configure the end calendar
-    endCal = Calendar.getInstance(timeZone)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    #endCal.add(Calendar.MONTH, -3)
-
-    # Calendar can be adjusted using the following functions:
-    #   startCal.set(Calendar.DATE, 1)          # Sets the date of the calendar.
-    #   startCal.set(Calendar.HOUR_OF_DAY, 1)   # Sets the hour of the day to 0100 (1-24)
-    #   startCal.set(Calendar.YEAR, 2020)       # Sets the year
-    #   startCal.set(Calendar.MONTH, 4)         # Sets the month (month 4 means May to Java)
+    end_date_dt = datetime.now(central).replace(minute=0, second=0, microsecond=0)
+    start_date_dt = end_date_dt - timedelta(days=5)
+    #start_date_dt = end_date_dt - timedelta(days=5, hours=7)
+
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
+
+    # Dates can be adjusted using normal datetime arithmetic/replace, e.g.:
+    #   start_date_dt = start_date_dt.replace(day=1)                  # start of month
+    #   start_date_dt = start_date_dt.replace(hour=1)                 # 0100 local time
+    #   start_date_dt = start_date_dt.replace(year=2020, month=5)     # month is 1-indexed here
 
     officeID = "SWT"
 
@@ -99,23 +92,23 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
 
     #
     #  GROUP 5 PROJECTS (SELF-TIMED TRANSMISSIONS WITHIN 19 TO 21 MINUTES PAST THE TOP OF THE HOUR)
     #
 
     #MCGE
-    gateCalc.computeFlowGroup("SWT", "MCGE",  startCal.getTime(), endCal.getTime(), "Flow.MCGE.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "MCGE",  startCal.getTime(), endCal.getTime(), "Flow.MCGE.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "MCGE",  start_date, end_date, "Flow.MCGE.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "MCGE",  start_date, end_date, "Flow.MCGE.Gated_Total")
 
     #BIGH
-    gateCalc.computeFlowGroup("SWT", "BIGH",  startCal.getTime(), endCal.getTime(), "Flow.BIGH.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "BIGH",  startCal.getTime(), endCal.getTime(), "Flow.BIGH.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "BIGH",  start_date, end_date, "Flow.BIGH.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "BIGH",  start_date, end_date, "Flow.BIGH.Gated_Total")
 
     #KEMP
-    gateCalc.computeFlowGroup("SWT", "KEMP",  startCal.getTime(), endCal.getTime(), "Flow.KEMP.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "KEMP",  startCal.getTime(), endCal.getTime(), "Flow.KEMP.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "KEMP",  start_date, end_date, "Flow.KEMP.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "KEMP",  start_date, end_date, "Flow.KEMP.Gated_Total")
 
 
 if __name__ == "__main__":
diff --git a/district-scripts/SWT/GateFlowGroup6.py b/district-scripts/SWT/GateFlowGroup6.py
index 933592d..c735906 100644
--- a/district-scripts/SWT/GateFlowGroup6.py
+++ b/district-scripts/SWT/GateFlowGroup6.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,37 +67,24 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
 
     # Defaults to start of the day 5 days ago, and ends at the top of the current hour today
-    # configure the start calendar
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    #startCal.add(Calendar.HOUR, -7)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-
-    #startCal.set(Calendar.YEAR, 2025)
-    #startCal.set(Calendar.MONTH, 0)   #e.g.  6 ==July
-    #startCal.set(Calendar.DAY_OF_MONTH, 14)
-
+    end_date_dt = datetime.now(central).replace(minute=0, second=0, microsecond=0)
+    start_date_dt = end_date_dt - timedelta(days=5)
+    #start_date_dt = end_date_dt - timedelta(days=5, hours=7)
 
-    # configure the end calendar
-    endCal = Calendar.getInstance(timeZone)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    #endCal.add(Calendar.MONTH, -3)
+    #start_date_dt = start_date_dt.replace(year=2025, month=1, day=14)  # month is 1-indexed here
 
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
 
-    # Calendar can be adjusted using the following functions:
-    #   startCal.set(Calendar.DATE, 1)          # Sets the date of the calendar.
-    #   startCal.set(Calendar.HOUR_OF_DAY, 1)   # Sets the hour of the day to 0100 (1-24)
-    #   startCal.set(Calendar.YEAR, 2020)       # Sets the year
-    #   startCal.set(Calendar.MONTH, 4)         # Sets the month (month 4 means May to Java)
+    # Dates can be adjusted using normal datetime arithmetic/replace, e.g.:
+    #   start_date_dt = start_date_dt.replace(day=1)                  # start of month
+    #   start_date_dt = start_date_dt.replace(hour=1)                 # 0100 local time
+    #   start_date_dt = start_date_dt.replace(year=2020, month=5)     # month is 1-indexed here
 
     officeID = "SWT"
 
@@ -105,7 +94,7 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
 
 
     #
@@ -113,40 +102,40 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     #
 
     #WDMA
-    gateCalc.computeFlowGroup("SWT", "WDMA",  startCal.getTime(), endCal.getTime(), "Flow.WDMA.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "WDMA",  startCal.getTime(), endCal.getTime(), "Flow.WDMA.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "WDMA",  start_date, end_date, "Flow.WDMA.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "WDMA",  start_date, end_date, "Flow.WDMA.Gated_Total")
 
     #WEBB
-    gateCalc.computeFlowGroup("SWT", "WEBB",  startCal.getTime(), endCal.getTime(), "Flow.WEBB.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "WEBB",  startCal.getTime(), endCal.getTime(), "Flow.WEBB.Turbine_Total")
-    gateCalc.computeFlowGroup("SWT", "WEBB",  startCal.getTime(), endCal.getTime(), "Flow.WEBB.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "WEBB",  start_date, end_date, "Flow.WEBB.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "WEBB",  start_date, end_date, "Flow.WEBB.Turbine_Total")
+    gateCalc.computeFlowGroup("SWT", "WEBB",  start_date, end_date, "Flow.WEBB.Gated_Total")
 
     #WIST
-    gateCalc.computeFlowGroup("SWT", "WIST",  startCal.getTime(), endCal.getTime(), "Flow.WIST.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "WIST",  startCal.getTime(), endCal.getTime(), "Flow.WIST.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "WIST",  start_date, end_date, "Flow.WIST.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "WIST",  start_date, end_date, "Flow.WIST.Gated_Total")
 
     #TENK
-    gateCalc.computeFlowGroup("SWT", "TENK",  startCal.getTime(), endCal.getTime(), "Flow.TENK.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "TENK",  startCal.getTime(), endCal.getTime(), "Flow.TENK.Turbine_Total")
-    gateCalc.computeFlowGroup("SWT", "TENK",  startCal.getTime(), endCal.getTime(), "Flow.TENK.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "TENK",  start_date, end_date, "Flow.TENK.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "TENK",  start_date, end_date, "Flow.TENK.Turbine_Total")
+    gateCalc.computeFlowGroup("SWT", "TENK",  start_date, end_date, "Flow.TENK.Gated_Total")
 
     #FGIB
-    gateCalc.computeFlowGroup("SWT", "FGIB",  startCal.getTime(), endCal.getTime(), "Flow.FGIB.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "FGIB",  startCal.getTime(), endCal.getTime(), "Flow.FGIB.Turbine_Total")
-    gateCalc.computeFlowGroup("SWT", "FGIB",  startCal.getTime(), endCal.getTime(), "Flow.FGIB.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "FGIB",  start_date, end_date, "Flow.FGIB.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "FGIB",  start_date, end_date, "Flow.FGIB.Turbine_Total")
+    gateCalc.computeFlowGroup("SWT", "FGIB",  start_date, end_date, "Flow.FGIB.Gated_Total")
 
     #THUN
-    gateCalc.computeFlowGroup("SWT", "THUN",  startCal.getTime(), endCal.getTime(), "Flow.THUN.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "THUN",  startCal.getTime(), endCal.getTime(), "Flow.THUN.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "THUN",  start_date, end_date, "Flow.THUN.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "THUN",  start_date, end_date, "Flow.THUN.Gated_Total")
 
     #GSAL
-    gateCalc.computeFlowGroup("SWT", "GSAL",  startCal.getTime(), endCal.getTime(), "Flow.GSAL.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "GSAL",  startCal.getTime(), endCal.getTime(), "Flow.GSAL.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "GSAL",  start_date, end_date, "Flow.GSAL.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "GSAL",  start_date, end_date, "Flow.GSAL.Gated_Total")
 
     #PENS
-    gateCalc.computeFlowGroup("SWT", "PENS",  startCal.getTime(), endCal.getTime(), "Flow.PENS.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "PENS",  startCal.getTime(), endCal.getTime(), "Flow.PENS.Turbine_Total")
-    gateCalc.computeFlowGroup("SWT", "PENS",  startCal.getTime(), endCal.getTime(), "Flow.PENS.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "PENS",  start_date, end_date, "Flow.PENS.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "PENS",  start_date, end_date, "Flow.PENS.Turbine_Total")
+    gateCalc.computeFlowGroup("SWT", "PENS",  start_date, end_date, "Flow.PENS.Gated_Total")
 
 
 
diff --git a/district-scripts/SWT/GateFlowGroup7.py b/district-scripts/SWT/GateFlowGroup7.py
index 21a0f89..d00ac37 100644
--- a/district-scripts/SWT/GateFlowGroup7.py
+++ b/district-scripts/SWT/GateFlowGroup7.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,32 +67,24 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
 
     # Defaults to start of the day 5 days ago, and ends at the top of the current hour today
-    # configure the start calendar
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    #startCal.add(Calendar.HOUR, -7)
+    end_date_dt = datetime.now(central).replace(minute=0, second=0, microsecond=0)
+    start_date_dt = end_date_dt - timedelta(days=5)
+    #start_date_dt = end_date_dt - timedelta(days=5, hours=7)
     #remove or comment out the next line when done!! it was for a big backload  ajm
-    #startCal.add(Calendar.MONTH, -10)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
+    #start_date_dt = start_date_dt - timedelta(days=305)  # ~10 months
 
-    # configure the end calendar
-    endCal = Calendar.getInstance(timeZone)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
 
-    # Calendar can be adjusted using the following functions:
-    #   startCal.set(Calendar.DATE, 1)          # Sets the date of the calendar.
-    #   startCal.set(Calendar.HOUR_OF_DAY, 1)   # Sets the hour of the day to 0100 (1-24)
-    #   startCal.set(Calendar.YEAR, 2020)       # Sets the year
-    #   startCal.set(Calendar.MONTH, 4)         # Sets the month (month 4 means May to Java)
+    # Dates can be adjusted using normal datetime arithmetic/replace, e.g.:
+    #   start_date_dt = start_date_dt.replace(day=1)                  # start of month
+    #   start_date_dt = start_date_dt.replace(hour=1)                 # 0100 local time
+    #   start_date_dt = start_date_dt.replace(year=2020, month=5)     # month is 1-indexed here
 
     officeID = "SWT"
 
@@ -100,7 +94,7 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
 
 
     #
@@ -108,36 +102,36 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     #
 
     #CHOU
-    gateCalc.computeFlowGroup("SWT", "CHOU",  startCal.getTime(), endCal.getTime(), "Flow.CHOU.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "CHOU",  startCal.getTime(), endCal.getTime(), "Flow.CHOU.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "CHOU",  start_date, end_date, "Flow.CHOU.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "CHOU",  start_date, end_date, "Flow.CHOU.Gated_Total")
 
     #NEWT
-    gateCalc.computeFlowGroup("SWT", "NEWT",  startCal.getTime(), endCal.getTime(), "Flow.NEWT.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "NEWT",  startCal.getTime(), endCal.getTime(), "Flow.NEWT.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "NEWT",  start_date, end_date, "Flow.NEWT.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "NEWT",  start_date, end_date, "Flow.NEWT.Gated_Total")
 
     #TOMS
-    gateCalc.computeFlowGroup("SWT", "TOMS",  startCal.getTime(), endCal.getTime(), "Flow.TOMS.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "TOMS",  startCal.getTime(), endCal.getTime(), "Flow.TOMS.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "TOMS",  start_date, end_date, "Flow.TOMS.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "TOMS",  start_date, end_date, "Flow.TOMS.Gated_Total")
 
     #TORO
-    gateCalc.computeFlowGroup("SWT", "TORO",  startCal.getTime(), endCal.getTime(), "Flow.TORO.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "TORO",  startCal.getTime(), endCal.getTime(), "Flow.TORO.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "TORO",  start_date, end_date, "Flow.TORO.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "TORO",  start_date, end_date, "Flow.TORO.Gated_Total")
 
     #ALTU
-    gateCalc.computeFlowGroup("SWT", "ALTU",  startCal.getTime(), endCal.getTime(), "Flow.ALTU.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "ALTU",  startCal.getTime(), endCal.getTime(), "Flow.ALTU.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "ALTU",  start_date, end_date, "Flow.ALTU.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "ALTU",  start_date, end_date, "Flow.ALTU.Gated_Total")
 
     #ELDR
-    gateCalc.computeFlowGroup("SWT", "ELDR",  startCal.getTime(), endCal.getTime(), "Flow.ELDR.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "ELDR",  startCal.getTime(), endCal.getTime(), "Flow.ELDR.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "ELDR",  start_date, end_date, "Flow.ELDR.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "ELDR",  start_date, end_date, "Flow.ELDR.Gated_Total")
 
     #CHEN
-    gateCalc.computeFlowGroup("SWT", "CHEN",  startCal.getTime(), endCal.getTime(), "Flow.CHEN.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "CHEN",  startCal.getTime(), endCal.getTime(), "Flow.CHEN.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "CHEN",  start_date, end_date, "Flow.CHEN.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "CHEN",  start_date, end_date, "Flow.CHEN.Gated_Total")
 
     #JOHN
-    gateCalc.computeFlowGroup("SWT", "JOHN",  startCal.getTime(), endCal.getTime(), "Flow.JOHN.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "JOHN",  startCal.getTime(), endCal.getTime(), "Flow.JOHN.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "JOHN",  start_date, end_date, "Flow.JOHN.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "JOHN",  start_date, end_date, "Flow.JOHN.Gated_Total")
 
 
 
diff --git a/district-scripts/SWT/GateFlowGroup8.py b/district-scripts/SWT/GateFlowGroup8.py
index 83c0b4b..6f30f0d 100644
--- a/district-scripts/SWT/GateFlowGroup8.py
+++ b/district-scripts/SWT/GateFlowGroup8.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,31 +67,22 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
 
     # Defaults to start of the day 5 days ago, and ends at the top of the current hour today
-    # configure the start calendar
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    #startCal.add(Calendar.HOUR, -7)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-
-    # configure the end calendar
-    endCal = Calendar.getInstance(timeZone)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    #endCal.add(Calendar.MONTH, -3)
-
-    # Calendar can be adjusted using the following functions:
-    #   startCal.set(Calendar.DATE, 1)          # Sets the date of the calendar.
-    #   startCal.set(Calendar.HOUR_OF_DAY, 1)   # Sets the hour of the day to 0100 (1-24)
-    #   startCal.set(Calendar.YEAR, 2020)       # Sets the year
-    #   startCal.set(Calendar.MONTH, 4)         # Sets the month (month 4 means May to Java)
+    end_date_dt = datetime.now(central).replace(minute=0, second=0, microsecond=0)
+    start_date_dt = end_date_dt - timedelta(days=5)
+    #start_date_dt = end_date_dt - timedelta(days=5, hours=7)
+
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
+
+    # Dates can be adjusted using normal datetime arithmetic/replace, e.g.:
+    #   start_date_dt = start_date_dt.replace(day=1)                  # start of month
+    #   start_date_dt = start_date_dt.replace(hour=1)                 # 0100 local time
+    #   start_date_dt = start_date_dt.replace(year=2020, month=5)     # month is 1-indexed here
 
     officeID = "SWT"
 
@@ -99,7 +92,7 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
 
 
     #
@@ -107,8 +100,8 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     #
 
     #MERE
-    gateCalc.computeFlowGroup("SWT", "MERE",  startCal.getTime(), endCal.getTime(), "Flow.MERE.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "MERE",  startCal.getTime(), endCal.getTime(), "Flow.MERE.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "MERE",  start_date, end_date, "Flow.MERE.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "MERE",  start_date, end_date, "Flow.MERE.Gated_Total")
 
 
 
diff --git a/district-scripts/SWT/GateFlowGroup9.py b/district-scripts/SWT/GateFlowGroup9.py
index 44550e5..98a595a 100644
--- a/district-scripts/SWT/GateFlowGroup9.py
+++ b/district-scripts/SWT/GateFlowGroup9.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,31 +67,22 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
 
     # Defaults to start of the day 5 days ago, and ends at the top of the current hour today
-    # configure the start calendar
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    #startCal.add(Calendar.HOUR, -7)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-
-    # configure the end calendar
-    endCal = Calendar.getInstance(timeZone)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    #endCal.add(Calendar.MONTH, -3)
-
-    # Calendar can be adjusted using the following functions:
-    #   startCal.set(Calendar.DATE, 1)          # Sets the date of the calendar.
-    #   startCal.set(Calendar.HOUR_OF_DAY, 1)   # Sets the hour of the day to 0100 (1-24)
-    #   startCal.set(Calendar.YEAR, 2020)       # Sets the year
-    #   startCal.set(Calendar.MONTH, 4)         # Sets the month (month 4 means May to Java)
+    end_date_dt = datetime.now(central).replace(minute=0, second=0, microsecond=0)
+    start_date_dt = end_date_dt - timedelta(days=5)
+    #start_date_dt = end_date_dt - timedelta(days=5, hours=7)
+
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
+
+    # Dates can be adjusted using normal datetime arithmetic/replace, e.g.:
+    #   start_date_dt = start_date_dt.replace(day=1)                  # start of month
+    #   start_date_dt = start_date_dt.replace(hour=1)                 # 0100 local time
+    #   start_date_dt = start_date_dt.replace(year=2020, month=5)     # month is 1-indexed here
 
     officeID = "SWT"
 
@@ -99,7 +92,7 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
 
 
     #
@@ -107,9 +100,9 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     #
 
     #KEYS
-    gateCalc.computeFlowGroup("SWT", "KEYS",  startCal.getTime(), endCal.getTime(), "Flow.KEYS.Project_Total")
-    gateCalc.computeFlowGroup("SWT", "KEYS",  startCal.getTime(), endCal.getTime(), "Flow.KEYS.Turbine_Total")
-    gateCalc.computeFlowGroup("SWT", "KEYS",  startCal.getTime(), endCal.getTime(), "Flow.KEYS.Gated_Total")
+    gateCalc.computeFlowGroup("SWT", "KEYS",  start_date, end_date, "Flow.KEYS.Project_Total")
+    gateCalc.computeFlowGroup("SWT", "KEYS",  start_date, end_date, "Flow.KEYS.Turbine_Total")
+    gateCalc.computeFlowGroup("SWT", "KEYS",  start_date, end_date, "Flow.KEYS.Gated_Total")
 
 
 
diff --git a/district-scripts/SWT/GateFlowHUDS-WS.py b/district-scripts/SWT/GateFlowHUDS-WS.py
index 4332238..4280dbe 100644
--- a/district-scripts/SWT/GateFlowHUDS-WS.py
+++ b/district-scripts/SWT/GateFlowHUDS-WS.py
@@ -2,30 +2,32 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
-    from java.util import TimeZone
     from usace.rowcps.headless import LoggingOptions
 
-    def compute_All_Flowgroups(officeID, location, startCal, endCal):
+
+    def compute_All_Flowgroups(officeID, location, start_date, end_date):
         # Takes in locations defined by user in group and computes all flow groups
         try:
-            gateCalc.computeAll(officeID, location, startCal.getTime(), endCal.getTime())
+            gateCalc.computeAll(officeID, location, start_date, end_date)
         except Exception as e:
             print("Error Computing all Flow Groups at {0} {1}".format(officeID, location))
             print(e)
             print('')
 
 
-    def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
+    def compute_Single_Flowgroup(officeID, location, start_date, end_date, flowGroup):
         try:
-            gateCalc.computeFlowGroup(officeID, location, startCal.getTime(), endCal.getTime(), "Flow.{0}.{1}".format(location, flowGroup))
+            gateCalc.computeFlowGroup(officeID, location, start_date, end_date, "Flow.{0}.{1}".format(location, flowGroup))
         except Exception as e:
             print("Error Computing Flow Group {0} at {1}".format(officeID, location))
             print(e)
             print('')
 
-        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  startCal.getTime(), endCal.getTime(), "Flow.ACTT2.Pump_Out_Total")
+        # #gateCalc.computeFlowGroup("SWF", "ACTT2",  start_date, end_date, "Flow.ACTT2.Pump_Out_Total")
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -65,33 +67,24 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    timeZone = TimeZone.getTimeZone("US/Central")
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
 
-    # Defaults to start of the day 5 days ago, and ends at the top of the current hour today
-    # configure the start calendar
-    startCal = Calendar.getInstance(timeZone)
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    startCal.add(Calendar.HOUR, -7)
+    # Defaults to start of the day 5 days and 7 hours ago, and ends at the top
+    # of the current hour today
+    end_date_dt = datetime.now(central).replace(minute=0, second=0, microsecond=0)
+    start_date_dt = end_date_dt - timedelta(days=5, hours=7)
     #remove or comment out the next line when done!! it was for a big backload  ajm
-    #startCal.add(Calendar.MONTH, -5)
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
+    #start_date_dt = start_date_dt - timedelta(days=152)  # ~5 months
 
-    # configure the end calendar
-    endCal = Calendar.getInstance(timeZone)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-    #endCal.add(Calendar.MONTH, -3)
+    start_date = start_date_dt.astimezone(timezone.utc)
+    end_date = end_date_dt.astimezone(timezone.utc)
 
-    # Calendar can be adjusted using the following functions:
-    #   startCal.set(Calendar.DATE, 1)          # Sets the date of the calendar.
-    #   startCal.set(Calendar.HOUR_OF_DAY, 1)   # Sets the hour of the day to 0100 (1-24)
-    #   startCal.set(Calendar.YEAR, 2020)       # Sets the year
-    #   startCal.set(Calendar.MONTH, 4)         # Sets the month (month 4 means May to Java)
+    # Dates can be adjusted using normal datetime arithmetic/replace, e.g.:
+    #   start_date_dt = start_date_dt.replace(day=1)                  # start of month
+    #   start_date_dt = start_date_dt.replace(hour=1)                 # 0100 local time
+    #   start_date_dt = start_date_dt.replace(year=2020, month=5)     # month is 1-indexed here
 
     officeID = "SWT"
 
@@ -101,11 +94,11 @@ def compute_Single_Flowgroup(officeID, location, startCal, endCal, flowGroup):
     # projectId
     # startDate
     # endDate
-    # gateCalc.computeFlowGroup("SWF", "LEWT2",  startCal.getTime(), endCal.getTime(), "Flow.LEWT2.ConduitGate_Total")
+    # gateCalc.computeFlowGroup("SWF", "LEWT2",  start_date, end_date, "Flow.LEWT2.ConduitGate_Total")
 
     #HUDS
-    gateCalc.computeFlowGroup("SWT", "HUDS",  startCal.getTime(), endCal.getTime(), "Flow.HUDS.Pump_Out_Total")
-    gateCalc.computeFlowGroup("SWT", "HUDS",  startCal.getTime(), endCal.getTime(), "Flow.HUDS.Pump_In_Total")
+    gateCalc.computeFlowGroup("SWT", "HUDS",  start_date, end_date, "Flow.HUDS.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "HUDS",  start_date, end_date, "Flow.HUDS.Pump_In_Total")
 
 
 
diff --git a/district-scripts/SWT/WaterSupplyFlowGroup.py b/district-scripts/SWT/WaterSupplyFlowGroup.py
index 8a7bb02..5fced69 100644
--- a/district-scripts/SWT/WaterSupplyFlowGroup.py
+++ b/district-scripts/SWT/WaterSupplyFlowGroup.py
@@ -2,10 +2,13 @@
 
 
 def run_calculations(registry):
+    from datetime import datetime, timedelta, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar
     from usace.rowcps.headless import LoggingOptions
 
+
     # Description of: LoggingOptions.setDbMessageLevel(int level)
     #
     # Adds Time Series logging messages in the OracleTimeSeriesDaoImpl.  Recommended
@@ -45,41 +48,35 @@ def run_calculations(registry):
     # this retrieves a Gate Flow calculation object
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
 
-    # the gate flow calculations requires a start and end time.
-    # here we create a java Calendar object that will be used to create the start Date
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time. (The previous Calendar.getInstance()
+    # calls here had no explicit timezone and silently depended on whatever
+    # timezone the host happened to be configured with.)
     #
     # use the current date minus 5 days.
     #
-    startCal = Calendar.getInstance()
-    #startCal.clear()
-    #startCal.set(Calendar.YEAR, 2016)
-    #startCal.set(Calendar.MONTH, 8)
-    startCal.add(Calendar.DAY_OF_MONTH, -5)
-    #startCal.set(Calendar.HOUR, 0) 
-    #startCal.add(Calendar.HOUR, -4) 
-    startCal.set(Calendar.MINUTE, 0)
-    startCal.set(Calendar.SECOND, 0)
-    startCal.set(Calendar.MILLISECOND, 0)
-
-    print("this is the place to write the startCal!")
-    print(startCal.getTime().toString())
-
-    # create a java Calendar object that will be used to create the end Date
+    central = ZoneInfo("America/Chicago")
+    end_date_dt = datetime.now(central).replace(minute=0, second=0, microsecond=0)
+    #end_date_dt = end_date_dt.replace(year=2016, month=9)  # month is 1-indexed here
+    start_date_dt = end_date_dt - timedelta(days=5)
+    #start_date_dt = start_date_dt.replace(hour=0)
+    #start_date_dt = start_date_dt - timedelta(hours=4)
+
+    start_date = start_date_dt.astimezone(timezone.utc)
+
+    print("this is the place to write the start_date!")
+    print(start_date.isoformat())
+
     # use the current date.
     #
-    endCal = Calendar.getInstance()
     #remove the next line when the headless time options are fixed
-    #endCal.add(Calendar.DAY_OF_MONTH, 1)  
-    #endCal.set(Calendar.HOUR, 16) 
-    #endCal.set(Calendar.YEAR, 2018)
-    #endCal.set(Calendar.MONTH, 6)
-    #endCal.set(Calendar.DAY_OF_MONTH, 6)
-    endCal.set(Calendar.MINUTE, 0)
-    endCal.set(Calendar.SECOND, 0)
-    endCal.set(Calendar.MILLISECOND, 0)
-
-    print("this is the place to write the endCal!")
-    print(endCal.getTime().toString())
+    #end_date_dt = end_date_dt + timedelta(days=1)
+    #end_date_dt = end_date_dt.replace(hour=16, year=2018, month=7, day=6)
+
+    end_date = end_date_dt.astimezone(timezone.utc)
+
+    print("this is the place to write the end_date!")
+    print(end_date.isoformat())
 
     # the gateCalc object can perform its calculation for a single flow group
     # the computeFlowGroup method takes:
@@ -95,43 +92,43 @@ def run_calculations(registry):
 
 
     #ARBU
-    gateCalc.computeFlowGroup("SWT", "ARBU",  startCal.getTime(), endCal.getTime(), "Flow.ARBU.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "ARBU",  start_date, end_date, "Flow.ARBU.Pump_Out_Total")
 
     #ARCA
-    gateCalc.computeFlowGroup("SWT", "ARCA",  startCal.getTime(), endCal.getTime(), "Flow.ARCA.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "ARCA",  start_date, end_date, "Flow.ARCA.Pump_Out_Total")
 
     #CHEN
-    gateCalc.computeFlowGroup("SWT", "CHEN",  startCal.getTime(), endCal.getTime(), "Flow.CHEN.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "CHEN",  start_date, end_date, "Flow.CHEN.Pump_Out_Total")
 
     #ELDR
-    gateCalc.computeFlowGroup("SWT", "ELDR",  startCal.getTime(), endCal.getTime(), "Flow.ELDR.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "ELDR",  start_date, end_date, "Flow.ELDR.Pump_Out_Total")
 
     #FCOB
-    gateCalc.computeFlowGroup("SWT", "FCOB",  startCal.getTime(), endCal.getTime(), "Flow.FCOB.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "FCOB",  start_date, end_date, "Flow.FCOB.Pump_Out_Total")
 
     #FOSS
-    gateCalc.computeFlowGroup("SWT", "FOSS",  startCal.getTime(), endCal.getTime(), "Flow.FOSS.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "FOSS",  start_date, end_date, "Flow.FOSS.Pump_Out_Total")
 
     #MCGE
-    gateCalc.computeFlowGroup("SWT", "MCGE",  startCal.getTime(), endCal.getTime(), "Flow.MCGE.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "MCGE",  start_date, end_date, "Flow.MCGE.Pump_Out_Total")
 
     #MERE
-    gateCalc.computeFlowGroup("SWT", "MERE",  startCal.getTime(), endCal.getTime(), "Flow.MERE.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "MERE",  start_date, end_date, "Flow.MERE.Pump_Out_Total")
 
     #OOLO
-    gateCalc.computeFlowGroup("SWT", "OOLO",  startCal.getTime(), endCal.getTime(), "Flow.OOLO.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "OOLO",  start_date, end_date, "Flow.OOLO.Pump_Out_Total")
 
     #PATM
-    gateCalc.computeFlowGroup("SWT", "PATM",  startCal.getTime(), endCal.getTime(), "Flow.PATM.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "PATM",  start_date, end_date, "Flow.PATM.Pump_Out_Total")
 
     #THUN
-    gateCalc.computeFlowGroup("SWT", "THUN",  startCal.getTime(), endCal.getTime(), "Flow.THUN.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "THUN",  start_date, end_date, "Flow.THUN.Pump_Out_Total")
 
     #TOMS
-    gateCalc.computeFlowGroup("SWT", "TOMS",  startCal.getTime(), endCal.getTime(), "Flow.TOMS.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "TOMS",  start_date, end_date, "Flow.TOMS.Pump_Out_Total")
 
     #WAUR
-    gateCalc.computeFlowGroup("SWT", "WAUR",  startCal.getTime(), endCal.getTime(), "Flow.WAUR.Pump_Out_Total")
+    gateCalc.computeFlowGroup("SWT", "WAUR",  start_date, end_date, "Flow.WAUR.Pump_Out_Total")
 
 
 
diff --git a/docs/JYTHON_TO_JPYPE_MIGRATION.md b/docs/JYTHON_TO_JPYPE_MIGRATION.md
index a291407..d7a36d7 100644
--- a/docs/JYTHON_TO_JPYPE_MIGRATION.md
+++ b/docs/JYTHON_TO_JPYPE_MIGRATION.md
@@ -48,14 +48,15 @@ from regi_python import regi_session, run_headless
 
 
 def run_calculations(registry):
-    from java.util import Calendar
-    from java.util import TimeZone
+    from datetime import datetime, timezone
+    from zoneinfo import ZoneInfo
 
     gateCalc = registry.getCalculation(1.0, "Gate Flow")
-    timeZone = TimeZone.getTimeZone("US/Central")
-    startCal = Calendar.getInstance(timeZone)
-    endCal = Calendar.getInstance(timeZone)
-    gateCalc.computeFlowGroup("SWT", "FOSS", startCal.getTime(), endCal.getTime(), "Flow.FOSS.Project_Total")
+
+    central = ZoneInfo("America/Chicago")
+    start_date = datetime(2015, 5, 1, tzinfo=central).astimezone(timezone.utc)
+    end_date = datetime(2015, 7, 1, tzinfo=central).astimezone(timezone.utc)
+    gateCalc.computeFlowGroup("SWT", "FOSS", start_date, end_date, "Flow.FOSS.Project_Total")
 
 
 if __name__ == "__main__":
@@ -63,6 +64,10 @@ if __name__ == "__main__":
         run_headless(run_calculations)
 ```
 
+Note that this example no longer imports anything from `java.util` at all. Date/time
+values are built entirely in Python and only cross into Java as plain `datetime`
+objects — see [Date and Time Handling](#date-and-time-handling) below.
+
 ## Translation Rules
 
 ### 1. Move Java imports inside the callback
@@ -115,6 +120,102 @@ if __name__ == "__main__":
         run_headless(run_calculations)
 ```
 
+### 7. Replace `java.util.Calendar`/`TimeZone` with `datetime`/`zoneinfo`
+
+Old scripts built `java.util.Date` objects with `Calendar.getInstance(TimeZone.getTimeZone(...))`.
+New scripts should build ordinary Python `datetime` objects with `zoneinfo.ZoneInfo` instead,
+and pass them straight into the Java call. See
+[Date and Time Handling](#date-and-time-handling) for the full pattern and the one
+timezone rule you must not skip.
+
+## Date and Time Handling
+
+The Scriptable calculation APIs (`ScriptableInflow`, `ScriptableGateSettings`,
+`ScriptableGateFlowCalc`) accept `java.time.Instant` parameters for start/end dates.
+(The old `java.util.Date`/`long` overloads still exist but are `@Deprecated` —
+prefer `Instant`.) JPype automatically converts a plain Python `datetime.datetime`
+into a Java `Instant` when the target parameter is declared as `Instant`, so **you
+do not need to construct any Java object yourself**. Build the date in Python and
+pass it directly:
+
+```python
+from datetime import datetime, timezone
+from zoneinfo import ZoneInfo
+
+central = ZoneInfo("America/Chicago")
+start_date = datetime(2018, 8, 1, tzinfo=central).astimezone(timezone.utc)
+```
+
+### The one rule: always convert to UTC before calling into Java
+
+JPype's automatic `datetime -> Instant` conversion does **not** look at the
+`tzinfo` on the value you pass — it takes whatever wall-clock fields the datetime
+has and treats them as if they were already UTC. If you hand it a
+timezone-aware-but-not-UTC datetime directly, you will get the wrong instant with
+no error or warning:
+
+```python
+central = ZoneInfo("America/Chicago")
+midnight_central = datetime(2015, 5, 1, tzinfo=central)   # 2015-05-01 00:00 CDT == 2015-05-01 05:00 UTC
+
+gateCalc.computeAll("SWF", "LEWT2", midnight_central, end_date)   # WRONG: silently treated as 00:00 UTC, 5 hours off
+```
+
+Always call `.astimezone(timezone.utc)` on the value before it crosses into a
+Java call, as shown in every example in this document. Once a datetime's wall
+clock actually represents UTC, JPype's conversion is exact and this is the only
+step required — no epoch-millis math, no manual `Instant` construction.
+
+This is also why the timezone must always be given explicitly with
+`zoneinfo.ZoneInfo("America/Chicago")` (or whatever the district's local zone
+is) rather than left off. The JVM's own default timezone is UTC, not the
+district's local time — a naive `datetime.now()` or a `datetime` built without
+`tzinfo` has no way to know it should mean "Central time," and some
+scripts that called `Calendar.getInstance()` with no `TimeZone` argument were
+silently relying on whatever timezone the host machine happened to have
+configured. Always pass `tzinfo=` explicitly when constructing the date.
+
+### Building relative dates ("N days ago", "top of the hour", etc.)
+
+Most district scripts compute a date relative to "now" rather than a fixed date.
+Use `datetime.now(tz)` plus `timedelta` arithmetic, then `.replace(...)` to zero
+out whichever fields need truncating — this mirrors what `Calendar.add()` /
+`Calendar.set()` used to do, and is safe across DST transitions the same way:
+
+```python
+from datetime import datetime, timedelta, timezone
+from zoneinfo import ZoneInfo
+
+central = ZoneInfo("America/Chicago")
+
+# "5 days ago at midnight" through "tomorrow at midnight"
+today_midnight = datetime.now(central).replace(hour=0, minute=0, second=0, microsecond=0)
+start_date = (today_midnight - timedelta(days=5)).astimezone(timezone.utc)
+end_date = (today_midnight + timedelta(days=1)).astimezone(timezone.utc)
+
+# "5 days ago at the top of the current hour" through "the top of the current hour"
+end_date_dt = datetime.now(central).replace(minute=0, second=0, microsecond=0)
+start_date_dt = end_date_dt - timedelta(days=5)
+start_date = start_date_dt.astimezone(timezone.utc)
+end_date = end_date_dt.astimezone(timezone.utc)
+```
+
+A couple of translation notes when porting the old `Calendar` field calls:
+
+| Old `Calendar` code | `datetime` equivalent |
+| --- | --- |
+| `cal.add(Calendar.DAY_OF_MONTH, -5)` | `dt - timedelta(days=5)` |
+| `cal.set(Calendar.HOUR_OF_DAY, 0)` + `MINUTE`/`SECOND`/`MILLISECOND` to `0` | `dt.replace(hour=0, minute=0, second=0, microsecond=0)` |
+| `cal.set(Calendar.MONTH, 4)` | `dt.replace(month=5)` — **`Calendar.MONTH` is 0-indexed** (4 == May); `datetime.month` is 1-indexed, so add 1 when porting a literal month value |
+| `cal.set(Calendar.HOUR, 0)` | Avoid porting this one directly — `Calendar.HOUR` is the 12-hour field and doesn't reliably mean midnight (it depends on the AM/PM already set on the calendar). Use `hour=0` on the `datetime`, which unambiguously means midnight. |
+
+### Using the `long` epoch-millis overloads
+
+`ScriptableGateFlowCalc.computeAll`/`computeFlowGroup` also has `long` (epoch
+milliseconds) overloads. These remain valid but are deprecated in favor of
+`Instant`; if you do need a raw millisecond value, get it from an
+already-UTC-normalized datetime: `int(start_date.timestamp() * 1000)`.
+
 ## Project-Specific Examples
 
 The current district scripts show the same migration shape across several script families:
diff --git a/regi-headless/src/main/java/usace/rowcps/headless/calculator/flowgroup/ScriptableGateFlowCalc.java b/regi-headless/src/main/java/usace/rowcps/headless/calculator/flowgroup/ScriptableGateFlowCalc.java
index 7d3d0a9..a8e53bf 100644
--- a/regi-headless/src/main/java/usace/rowcps/headless/calculator/flowgroup/ScriptableGateFlowCalc.java
+++ b/regi-headless/src/main/java/usace/rowcps/headless/calculator/flowgroup/ScriptableGateFlowCalc.java
@@ -1,5 +1,6 @@
 package usace.rowcps.headless.calculator.flowgroup;
 
+import java.time.Instant;
 import java.util.Date;
 
 /**
@@ -9,16 +10,55 @@
 public interface ScriptableGateFlowCalc
 {
 
+	/**
+	 * @deprecated Use {@link #computeAll(String, String, Instant, Instant)} instead. java.util.Date
+	 * requires callers to build a java.util.Calendar with an explicit TimeZone to avoid relying on
+	 * the JVM's default timezone; Instant is an unambiguous point in time.
+	 */
+	@Deprecated
 	void computeAll(String officeId, String locationId, Date start, Date end);
+	/**
+	 * @deprecated Use {@link #computeAll(String, String, Instant, Instant)} instead. A bare epoch-millis
+	 * long has no explicit unit/type safety in scripts; Instant is self-documenting.
+	 */
+	@Deprecated
 	void computeAll(String officeId, String locationId, long startTime, long endTime);
+	void computeAll(String officeId, String locationId, Instant start, Instant end);
 
+	/**
+	 * @deprecated Use {@link #computeAll(String, String[], Instant, Instant)} instead.
+	 */
+	@Deprecated
 	void computeAll(String officeId, String[] locationIds, Date start, Date end);
+	/**
+	 * @deprecated Use {@link #computeAll(String, String[], Instant, Instant)} instead.
+	 */
+	@Deprecated
 	void computeAll(String officeId, String[] locationIds, long startTime, long endTime);
+	void computeAll(String officeId, String[] locationIds, Instant start, Instant end);
 
+	/**
+	 * @deprecated Use {@link #computeFlowGroup(String, String, Instant, Instant, String)} instead.
+	 */
+	@Deprecated
 	void computeFlowGroup(String officeId, String locationId, Date start, Date end, String groupId);
+	/**
+	 * @deprecated Use {@link #computeFlowGroup(String, String, Instant, Instant, String)} instead.
+	 */
+	@Deprecated
 	void computeFlowGroup(String officeId, String locationId, long startTime, long endTime, String groupId);
+	void computeFlowGroup(String officeId, String locationId, Instant start, Instant end, String groupId);
 
+	/**
+	 * @deprecated Use {@link #computeFlowGroup(String, String[], Instant, Instant, String)} instead.
+	 */
+	@Deprecated
 	void computeFlowGroup(String officeId, String[] locationIds, Date start, Date end, String groupId);
+	/**
+	 * @deprecated Use {@link #computeFlowGroup(String, String[], Instant, Instant, String)} instead.
+	 */
+	@Deprecated
 	void computeFlowGroup(String officeId, String[] locationIds, long startTime, long endTime, String groupId);
+	void computeFlowGroup(String officeId, String[] locationIds, Instant start, Instant end, String groupId);
 
 }
diff --git a/regi-headless/src/main/java/usace/rowcps/headless/calculator/flowgroup/ScriptableGateFlowImpl.java b/regi-headless/src/main/java/usace/rowcps/headless/calculator/flowgroup/ScriptableGateFlowImpl.java
index f50932f..a5001f2 100644
--- a/regi-headless/src/main/java/usace/rowcps/headless/calculator/flowgroup/ScriptableGateFlowImpl.java
+++ b/regi-headless/src/main/java/usace/rowcps/headless/calculator/flowgroup/ScriptableGateFlowImpl.java
@@ -5,6 +5,7 @@
 import hec.data.project.IProject;
 import hec.db.DbConnectionException;
 import hec.db.DbIoException;
+import java.time.Instant;
 import java.util.Calendar;
 import java.util.Date;
 import java.util.Map;
@@ -44,6 +45,13 @@ public void computeAll(String officeId, String locationId, Date start, Date end)
 
 	}
 
+	@Override
+	public void computeAll(String officeId, String locationId, Instant start, Instant end) {
+
+		computeAll(officeId, locationId, start.toEpochMilli(), end.toEpochMilli());
+
+	}
+
 	@Override
 	public void computeAll(String officeId, String locationId, long startTime, long endTime) {
             
@@ -88,6 +96,13 @@ public void computeAll(String officeId, String[] locationIds, Date start, Date e
 		}
 	}
 
+	@Override
+	public void computeAll(String officeId, String[] locationIds, Instant start, Instant end) {
+		for (String locationId : locationIds) {
+			computeAll(officeId, locationId, start, end);
+		}
+	}
+
 	@Override
 	public void computeAll(String officeId, String[] locationIds, long startTime, long endTime) {
 		for (String locationId : locationIds) {
@@ -102,6 +117,11 @@ public void computeFlowGroup(String officeId, String locationId, Date start, Dat
 		computeFlowGroup(officeId, locationId, startTime, endTime, groupId);
 	}
 
+	@Override
+	public void computeFlowGroup(String officeId, String locationId, Instant start, Instant end, String groupId) {
+		computeFlowGroup(officeId, locationId, start.toEpochMilli(), end.toEpochMilli(), groupId);
+	}
+
 	@Override
 	public void computeFlowGroup(String officeId, String locationId, long startTime, long endTime, String groupId) {
 		
@@ -150,6 +170,15 @@ public void computeFlowGroup(String officeId, String[] locationIds, Date start,
 		}
 	}
 
+	@Override
+	public void computeFlowGroup(String officeId, String[] locationIds, Instant start, Instant end, String groupId) {
+		long startTime = start.toEpochMilli();
+		long endTime = end.toEpochMilli();
+		for (String locationId : locationIds) {
+			computeFlowGroup(officeId, locationId, startTime, endTime, groupId);
+		}
+	}
+
 	@Override
 	public void computeFlowGroup(String officeId, String[] locationIds, long startTime, long endTime, String groupId) {
 		for (String locationId : locationIds) {
diff --git a/regi-headless/src/main/java/usace/rowcps/headless/calculator/gatesettings/ScriptableGateSettings.java b/regi-headless/src/main/java/usace/rowcps/headless/calculator/gatesettings/ScriptableGateSettings.java
index d8ec218..dab3685 100644
--- a/regi-headless/src/main/java/usace/rowcps/headless/calculator/gatesettings/ScriptableGateSettings.java
+++ b/regi-headless/src/main/java/usace/rowcps/headless/calculator/gatesettings/ScriptableGateSettings.java
@@ -1,5 +1,6 @@
 package usace.rowcps.headless.calculator.gatesettings;
 
+import java.time.Instant;
 import java.util.Date;
 
 /**
@@ -8,8 +9,33 @@
  */
 interface ScriptableGateSettings
 {
+	/**
+	 * @deprecated Use {@link #createGateSettings(String, String, Instant, Instant)} instead. java.util.Date
+	 * requires callers to build a java.util.Calendar with an explicit TimeZone to avoid relying on the JVM's
+	 * default timezone; Instant is an unambiguous point in time.
+	 */
+	@Deprecated
 	void createGateSettings(String officeId, String locationStr, Date startDate, Date end) throws Exception;
+	void createGateSettings(String officeId, String locationStr, Instant startDate, Instant end) throws Exception;
+
+	/**
+	 * @deprecated Use {@link #createGateSettingsGroup(String, String, Instant, Instant, String)} instead.
+	 */
+	@Deprecated
 	void createGateSettingsGroup(String officeId, String locationStr, Date startDate, Date end, String groupId) throws Exception;
+	void createGateSettingsGroup(String officeId, String locationStr, Instant startDate, Instant end, String groupId) throws Exception;
+
+	/**
+	 * @deprecated Use {@link #createGateSettingsOutlet(String, String, Instant, Instant, String)} instead.
+	 */
+	@Deprecated
 	void createGateSettingsOutlet(String officeId, String locationStr, Date startDate, Date end, String outletId) throws Exception;
+	void createGateSettingsOutlet(String officeId, String locationStr, Instant startDate, Instant end, String outletId) throws Exception;
+
+	/**
+	 * @deprecated Use {@link #createGateSettingsOutletFromTs(String, String, Instant, Instant, String, String)} instead.
+	 */
+	@Deprecated
 	void createGateSettingsOutletFromTs(String officeId, String locationStr, Date startDate, Date end, String outletId, String tsId) throws Exception;
+	void createGateSettingsOutletFromTs(String officeId, String locationStr, Instant startDate, Instant end, String outletId, String tsId) throws Exception;
 }
diff --git a/regi-headless/src/main/java/usace/rowcps/headless/calculator/gatesettings/ScriptableGateSettingsImpl.java b/regi-headless/src/main/java/usace/rowcps/headless/calculator/gatesettings/ScriptableGateSettingsImpl.java
index 3c2bffd..f5b7863 100644
--- a/regi-headless/src/main/java/usace/rowcps/headless/calculator/gatesettings/ScriptableGateSettingsImpl.java
+++ b/regi-headless/src/main/java/usace/rowcps/headless/calculator/gatesettings/ScriptableGateSettingsImpl.java
@@ -37,6 +37,7 @@
 import java.text.MessageFormat;
 import java.text.NumberFormat;
 import java.text.SimpleDateFormat;
+import java.time.Instant;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -109,6 +110,12 @@ public ScriptableGateSettingsImpl(RegiDomain regiDomain, ManagerId managerId) {
 		super(regiDomain, managerId);
 	}
 
+	@Override
+	public void createGateSettings(String officeId, String locationStr, Instant startDate, Instant end) throws Exception
+	{
+		createGateSettings(officeId, locationStr, Date.from(startDate), Date.from(end));
+	}
+
 	@Override
 	public void createGateSettings(String officeId, String locationStr, Date startDate, Date end) throws Exception
 	{
@@ -141,6 +148,12 @@ public void createGateSettings(String officeId, String locationStr, Date startDa
 		gc.saveData(options);
 	}
 
+	@Override
+	public void createGateSettingsOutlet(String officeId, String locationStr, Instant startDate, Instant end, String outletId) throws Exception
+	{
+		createGateSettingsOutlet(officeId, locationStr, Date.from(startDate), Date.from(end), outletId);
+	}
+
 	@Override
 	public void createGateSettingsOutlet(String officeId, String locationStr, Date startDate, Date end, String outletId) throws Exception
 	{
@@ -185,6 +198,13 @@ public void createGateSettingsOutlet(String officeId, String locationStr, Date s
 		gc.saveData(options);
 	}
 
+	@Override
+	public void createGateSettingsOutletFromTs(String officeId, String locationStr, Instant startDate, Instant end, String outletId, String tsId)
+			throws Exception
+	{
+		createGateSettingsOutletFromTs(officeId, locationStr, Date.from(startDate), Date.from(end), outletId, tsId);
+	}
+
 	@Override
 	public void createGateSettingsOutletFromTs(String officeId, String locationStr, Date startDate, Date end, String outletId, String tsId)
 			throws Exception
@@ -223,6 +243,12 @@ public IControlledOutlet getIControlledOutlet(GateCache gc, String outletId) {
 		return retval;
 	}
 
+	@Override
+	public void createGateSettingsGroup(String officeId, String locationStr, Instant startDate, Instant end, String groupId) throws Exception
+	{
+		createGateSettingsGroup(officeId, locationStr, Date.from(startDate), Date.from(end), groupId);
+	}
+
 	@Override
 	public void createGateSettingsGroup(String officeId, String locationStr, Date startDate, Date end, String groupId) throws Exception
 	{
diff --git a/regi-headless/src/main/java/usace/rowcps/headless/calculator/inflow/ScriptableInflow.java b/regi-headless/src/main/java/usace/rowcps/headless/calculator/inflow/ScriptableInflow.java
index d85f0b9..7c28488 100644
--- a/regi-headless/src/main/java/usace/rowcps/headless/calculator/inflow/ScriptableInflow.java
+++ b/regi-headless/src/main/java/usace/rowcps/headless/calculator/inflow/ScriptableInflow.java
@@ -1,5 +1,6 @@
 package usace.rowcps.headless.calculator.inflow;
 
+import java.time.Instant;
 import java.util.Date;
 
 /**
@@ -9,19 +10,63 @@
 public interface ScriptableInflow
 {
 
+	/**
+	 * @deprecated Use {@link #autoAdjust(String, String, Instant)} instead. java.util.Date
+	 * requires callers to build a java.util.Calendar with an explicit TimeZone to avoid
+	 * relying on the JVM's default timezone; Instant is an unambiguous point in time.
+	 */
+	@Deprecated
 	void autoAdjust(String officeId, String locationStr, Date startDate);
 
+	void autoAdjust(String officeId, String locationStr, Instant startDate);
+
+	/**
+	 * @deprecated Use {@link #autoAdjust(String, String, Instant, boolean, boolean)} instead.
+	 */
+	@Deprecated
 	void autoAdjust(String officeId, String locationStr, Date startDate, boolean useLimits, boolean freezeRain);
 
+	void autoAdjust(String officeId, String locationStr, Instant startDate, boolean useLimits, boolean freezeRain);
+
+	/**
+	 * @deprecated Use {@link #cloneInflows(String, String, Instant)} instead.
+	 */
+	@Deprecated
 	void cloneInflows(String officeId, String locationStr, Date startDate);
 
+	void cloneInflows(String officeId, String locationStr, Instant startDate);
+
+	/**
+	 * @deprecated Use {@link #zeroNegatives(String, String, Instant)} instead.
+	 */
+	@Deprecated
 	void zeroNegatives(String officeId, String locationStr, Date startDate);
 
+	void zeroNegatives(String officeId, String locationStr, Instant startDate);
+
+	/**
+	 * @deprecated Use {@link #balanceAll(String, String, Instant)} instead.
+	 */
+	@Deprecated
 	void balanceAll(String officeId, String locationStr, Date startDate);
 
+	void balanceAll(String officeId, String locationStr, Instant startDate);
+
+	/**
+	 * @deprecated Use {@link #computeInflow(String, String, Instant, Instant)} instead.
+	 */
+	@Deprecated
 	void computeInflow(String officeId, String locationStr, Date startDate, Date endDate);
 
+	void computeInflow(String officeId, String locationStr, Instant startDate, Instant endDate);
+
+	/**
+	 * @deprecated Use {@link #computeEvapAsFlow(String, String, Instant, Instant)} instead.
+	 */
+	@Deprecated
 	void computeEvapAsFlow(String officeId, String locationStr, Date startDate, Date endDate);
 
+	void computeEvapAsFlow(String officeId, String locationStr, Instant startDate, Instant endDate);
+
 	void setComputationStorageOptions(InflowComputationStorageOption option, InflowComputationStorageOption... options);
 }
diff --git a/regi-headless/src/main/java/usace/rowcps/headless/calculator/inflow/ScriptableInflowImpl.java b/regi-headless/src/main/java/usace/rowcps/headless/calculator/inflow/ScriptableInflowImpl.java
index b680a5c..bd10556 100644
--- a/regi-headless/src/main/java/usace/rowcps/headless/calculator/inflow/ScriptableInflowImpl.java
+++ b/regi-headless/src/main/java/usace/rowcps/headless/calculator/inflow/ScriptableInflowImpl.java
@@ -6,6 +6,7 @@
 import hec.db.DbConnectionException;
 import hec.db.DbException;
 import hec.db.DbIoException;
+import java.time.Instant;
 import java.util.Calendar;
 import java.util.Date;
 import java.util.HashMap;
@@ -63,6 +64,18 @@ public void autoAdjust(String officeId, String locationStr, Date startDate)
 		autoAdjust(officeId, locationStr, startDate, false, false);
 	}
 
+	@Override
+	public void autoAdjust(String officeId, String locationStr, Instant startDate)
+	{
+		autoAdjust(officeId, locationStr, Date.from(startDate), false, false);
+	}
+
+	@Override
+	public void autoAdjust(String officeId, String locationStr, Instant startDate, boolean useLimits, boolean freezeRain)
+	{
+		autoAdjust(officeId, locationStr, Date.from(startDate), useLimits, freezeRain);
+	}
+
 	@Override
 	public void autoAdjust(String officeId, String locationStr, Date startDate, boolean useLimits, boolean freezeRain)
 	{
@@ -111,6 +124,12 @@ public void autoAdjust(String officeId, String locationStr, Date startDate, bool
 		}
 	}
 
+	@Override
+	public void cloneInflows(String officeId, String locationStr, Instant startDate)
+	{
+		cloneInflows(officeId, locationStr, Date.from(startDate));
+	}
+
 	@Override
 	public void cloneInflows(String officeId, String locationStr, Date startDate)
 	{
@@ -150,6 +169,12 @@ public void cloneInflows(String officeId, String locationStr, Date startDate)
 		}
 	}
 
+	@Override
+	public void zeroNegatives(String officeId, String locationStr, Instant startDate)
+	{
+		zeroNegatives(officeId, locationStr, Date.from(startDate));
+	}
+
 	@Override
 	public void zeroNegatives(String officeId, String locationStr, Date startDate)
 	{
@@ -188,6 +213,12 @@ public void zeroNegatives(String officeId, String locationStr, Date startDate)
 		}
 	}
 
+	@Override
+	public void balanceAll(String officeId, String locationStr, Instant startDate)
+	{
+		balanceAll(officeId, locationStr, Date.from(startDate));
+	}
+
 	@Override
 	public void balanceAll(String officeId, String locationStr, Date startDate)
 	{
@@ -323,6 +354,12 @@ private InflowAdjustedTypeModel getOrCreateStatusMap(LocationTemplate template)
 		return retval;
 	}
 
+	@Override
+	public void computeEvapAsFlow(String officeId, String locationStr, Instant startDate, Instant endDate)
+	{
+		computeEvapAsFlow(officeId, locationStr, Date.from(startDate), Date.from(endDate));
+	}
+
 	@Override
 	public void computeEvapAsFlow(String officeId, String locationStr, Date startDate, Date endDate)
 	{
@@ -355,6 +392,12 @@ public void computeEvapAsFlow(String officeId, String locationStr, Date startDat
 		}
 	}
 
+	@Override
+	public void computeInflow(String officeId, String locationStr, Instant startDate, Instant endDate)
+	{
+		computeInflow(officeId, locationStr, Date.from(startDate), Date.from(endDate));
+	}
+
 	@Override
 	public void computeInflow(String officeId, String locationStr, Date startDate, Date endDate)
 	{
diff --git a/regi-headless/src/test/python/test_datetime_instant_conversion.py b/regi-headless/src/test/python/test_datetime_instant_conversion.py
new file mode 100644
index 0000000..73829f5
--- /dev/null
+++ b/regi-headless/src/test/python/test_datetime_instant_conversion.py
@@ -0,0 +1,90 @@
+"""
+Verifies JPype's automatic conversion of a plain Python `datetime.datetime`
+into a `java.time.Instant`, and locks in the exact timezone behavior documented
+in docs/JYTHON_TO_JPYPE_MIGRATION.md ("Date and Time Handling").
+
+These tests start a real JVM through jpype instead of faking `java.time`,
+because the point is to verify jpype's own conversion behavior rather than
+our code. They only touch `java.time.Instant`, which ships in every JDK/JRE,
+so no project jars or Gradle build are required -- just a JVM that jpype can
+locate. If none is available, the module is skipped rather than failed.
+"""
+
+from datetime import datetime, timezone
+
+import pytest
+
+jpype = pytest.importorskip("jpype")
+pytest.importorskip("jpype.imports")  # registers the `from java.x import Y` import hook
+
+
+def _ensure_jvm_started():
+    if jpype.isJVMStarted():
+        return
+    try:
+        jpype.startJVM(jpype.getDefaultJVMPath())
+    except Exception as exc:  # pragma: no cover - environment dependent
+        pytest.skip(f"No usable JVM available for jpype: {exc}")
+
+
+@pytest.fixture(scope="module", autouse=True)
+def _jvm():
+    _ensure_jvm_started()
+    yield
+    # Deliberately not shut down: a JVM cannot be restarted once stopped in
+    # the same process, and other test modules in this pytest run may still
+    # need one (real or mocked).
+
+
+@pytest.fixture(scope="module")
+def Instant():
+    from java.time import Instant as JInstant
+
+    return JInstant
+
+
+def test_utc_aware_datetime_converts_to_the_exact_instant(Instant):
+    """
+    A datetime whose wall-clock fields already represent UTC crosses into an
+    `Instant`-typed parameter exactly.
+
+    `compareTo`'s formal parameter type is declared as exactly `Instant`,
+    which is what makes jpype's datetime -> Instant converter fire. Methods
+    declared to accept `Object` (like `equals`) do NOT trigger it.
+    """
+    utc_dt = datetime(2018, 8, 1, 12, 30, 0, tzinfo=timezone.utc)
+    expected = Instant.parse("2018-08-01T12:30:00Z")
+
+    assert expected.compareTo(utc_dt) == 0
+
+
+def test_non_utc_aware_datetime_is_silently_misread_as_utc(Instant):
+    """
+    Regression guard for the one rule called out in the migration doc: jpype's
+    converter does not consult `tzinfo` -- it takes whatever wall-clock fields
+    the datetime has and stamps them as UTC. A Central-time datetime that is
+    NOT first normalized with `.astimezone(timezone.utc)` silently produces
+    the wrong instant, five hours off, with no error or warning.
+    """
+    from zoneinfo import ZoneInfo
+
+    central = ZoneInfo("America/Chicago")
+    midnight_central = datetime(2015, 5, 1, 0, 0, 0, tzinfo=central)  # really 05:00 UTC
+
+    what_jpype_actually_produces = Instant.parse("2015-05-01T00:00:00Z")
+    what_it_should_have_meant = Instant.parse("2015-05-01T05:00:00Z")
+
+    assert what_jpype_actually_produces.compareTo(midnight_central) == 0
+    assert what_it_should_have_meant.compareTo(midnight_central) != 0
+
+
+def test_astimezone_utc_before_passing_is_the_correct_pattern(Instant):
+    """The documented fix: always call `.astimezone(timezone.utc)` first."""
+    from zoneinfo import ZoneInfo
+
+    central = ZoneInfo("America/Chicago")
+    midnight_central = datetime(2015, 5, 1, 0, 0, 0, tzinfo=central)
+    normalized = midnight_central.astimezone(timezone.utc)
+
+    correct_instant = Instant.parse("2015-05-01T05:00:00Z")
+    assert correct_instant.compareTo(normalized) == 0
diff --git a/regi-headless/src/test/resources/usace/rowcps/headless/examples/GateFlowCalc.py b/regi-headless/src/test/resources/usace/rowcps/headless/examples/GateFlowCalc.py
index 8bcbab8..c7c3205 100644
--- a/regi-headless/src/test/resources/usace/rowcps/headless/examples/GateFlowCalc.py
+++ b/regi-headless/src/test/resources/usace/rowcps/headless/examples/GateFlowCalc.py
@@ -5,9 +5,12 @@
 
 
 def calculate_gate_flow(registry):
+    from datetime import datetime, timezone
+    from zoneinfo import ZoneInfo
+
     # Java imports must happen after regi_session starts the JVM.
     from java.lang import System
-    from java.util import Calendar, TimeZone
+
 
     print("Now executing GateFlowCalc.py")
     print("os.arch:", System.getProperty("os.arch"))
@@ -23,23 +26,19 @@ def calculate_gate_flow(registry):
     project_id = "LEWT2"
     flow_group_id = "Flow.LEWT2.ConduitGate_Total"
 
-    # Time zone must be set because the Solaris time zone is UTC
-    time_zone = TimeZone.getTimeZone("US/Central")
-    start_cal = Calendar.getInstance(time_zone)
-    start_cal.clear()
-    start_cal.set(Calendar.YEAR, 2015)
-    start_cal.set(Calendar.MONTH, 1)
-
-    end_cal = Calendar.getInstance(time_zone)
-    end_cal.clear()
-    end_cal.set(Calendar.YEAR, 2013)
-    end_cal.set(Calendar.MONTH, 1)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    # Java's Calendar.MONTH was 0-indexed (1 == February); datetime.month is
+    # 1-indexed, so we use 2 here for the same dates.
+    start_date = (datetime(2015, 2, 1, tzinfo=central)).astimezone(timezone.utc)
+    end_date = (datetime(2013, 2, 1, tzinfo=central)).astimezone(timezone.utc)
 
     gate_calc.computeFlowGroup(
         office_id,
         project_id,
-        start_cal.getTimeInMillis(),
-        end_cal.getTimeInMillis(),
+        start_date,
+        end_date,
         flow_group_id,
     )
 
diff --git a/regi-headless/src/test/resources/usace/rowcps/headless/examples/GateFlowCalc2.py b/regi-headless/src/test/resources/usace/rowcps/headless/examples/GateFlowCalc2.py
index 1eca4b1..14fc1ed 100644
--- a/regi-headless/src/test/resources/usace/rowcps/headless/examples/GateFlowCalc2.py
+++ b/regi-headless/src/test/resources/usace/rowcps/headless/examples/GateFlowCalc2.py
@@ -2,27 +2,24 @@
 
 
 def calculate_gate_flow(registry):
-    # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar, TimeZone
+    from datetime import datetime, timezone
+    from zoneinfo import ZoneInfo
+
 
     names = registry.getNames(1.0)
     print("names", names)
 
     gate_calc = registry.getCalculation(1.0, "Gate Flow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    time_zone = TimeZone.getTimeZone("US/Central")
-    start_cal = Calendar.getInstance(time_zone)
-    start_cal.clear()
-    start_cal.set(Calendar.YEAR, 2015)
-    start_cal.set(Calendar.MONTH, 4)
-
-    end_cal = Calendar.getInstance(time_zone)
-    end_cal.clear()
-    end_cal.set(Calendar.YEAR, 2015)
-    end_cal.set(Calendar.MONTH, 6)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    # Java's Calendar.MONTH was 0-indexed (4 == May, 6 == July); datetime.month
+    # is 1-indexed, so we use 5 and 7 here for the same dates.
+    start_date = (datetime(2015, 5, 1, tzinfo=central)).astimezone(timezone.utc)
+    end_date = (datetime(2015, 7, 1, tzinfo=central)).astimezone(timezone.utc)
 
-    gate_calc.computeAll("SWF", "LEWT2", start_cal.getTimeInMillis(), end_cal.getTimeInMillis())
+    gate_calc.computeAll("SWF", "LEWT2", start_date, end_date)
 
 
 if __name__ == "__main__":
diff --git a/regi-headless/src/test/resources/usace/rowcps/headless/examples/GateSettings.py b/regi-headless/src/test/resources/usace/rowcps/headless/examples/GateSettings.py
index b1d4121..c3a0995 100644
--- a/regi-headless/src/test/resources/usace/rowcps/headless/examples/GateSettings.py
+++ b/regi-headless/src/test/resources/usace/rowcps/headless/examples/GateSettings.py
@@ -2,43 +2,38 @@
 
 
 def calculate_gate_settings(registry):
-    # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar, TimeZone
+    from datetime import datetime, timezone
+    from zoneinfo import ZoneInfo
+
 
     # this gets a scriptable Gate Settings object
     gate_settings = registry.getCalculation(1.0, "Gate Settings")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    time_zone = TimeZone.getTimeZone("US/Central")
-    # configure the start calendar
-    start_cal = Calendar.getInstance(time_zone)
-    start_cal.clear()
-    start_cal.set(Calendar.YEAR, 2015)
-    start_cal.set(Calendar.MONTH, 4)
-
-    # configure the end calendar
-    end_cal = Calendar.getInstance(time_zone)
-    end_cal.clear()
-    end_cal.set(Calendar.YEAR, 2015)
-    end_cal.set(Calendar.MONTH, 6)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    # Java's Calendar.MONTH was 0-indexed (4 == May, 6 == July); datetime.month
+    # is 1-indexed, so we use 5 and 7 here for the same dates.
+    start_date = (datetime(2015, 5, 1, tzinfo=central)).astimezone(timezone.utc)
+    end_date = (datetime(2015, 7, 1, tzinfo=central)).astimezone(timezone.utc)
 
     # gate_settings contains four callable methods
-    #   void createGateSettings(String officeId, String locationStr, Date startDate, Date end) throws Exception;
-    #   void createGateSettingsGroup(String officeId, String locationStr, Date startDate, Date end, String groupId) throws Exception;
-    #   void createGateSettingsOutlet(String officeId, String locationStr, Date startDate, Date end, String outletId) throws Exception;
-    #   void createGateSettingsOutletFromTs(String officeId, String locationStr, Date startDate, Date end, String outletId, String tsId) throws Exception;
+    #   void createGateSettings(String officeId, String locationStr, Instant startDate, Instant end) throws Exception;
+    #   void createGateSettingsGroup(String officeId, String locationStr, Instant startDate, Instant end, String groupId) throws Exception;
+    #   void createGateSettingsOutlet(String officeId, String locationStr, Instant startDate, Instant end, String outletId) throws Exception;
+    #   void createGateSettingsOutletFromTs(String officeId, String locationStr, Instant startDate, Instant end, String outletId, String tsId) throws Exception;
 
     # This is an example of a call that would create gate settings at TainterGate 1 at WTYT2 from the specified input time series.
-    gate_settings.createGateSettingsOutletFromTs("SWF", "WTYT2", start_cal.getTime(), end_cal.getTime(), "TG1", "WTYT2-TG1.Opening-Spillway_Gate.Const.0.0.MANUAL")
+    gate_settings.createGateSettingsOutletFromTs("SWF", "WTYT2", start_date, end_date, "TG1", "WTYT2-TG1.Opening-Spillway_Gate.Const.0.0.MANUAL")
 
     # This is an example of a call that would create gate settings at TainterGate 1 at WTYT2 from the regi association configured input time series.
-    gate_settings.createGateSettingsOutlet("SWF", "WTYT2", start_cal.getTime(), end_cal.getTime(), "TG1")
+    gate_settings.createGateSettingsOutlet("SWF", "WTYT2", start_date, end_date, "TG1")
 
     # This is an example of a call that would create gate settings at all outlets at WTYT2 which are in the TainterGateWTY group from the association configured time series.
-    gate_settings.createGateSettingsGroup("SWF", "WTYT2", start_cal.getTime(), end_cal.getTime(), "WTYT2-TainterGateWTY")
+    gate_settings.createGateSettingsGroup("SWF", "WTYT2", start_date, end_date, "WTYT2-TainterGateWTY")
 
     # This is an example of a call that would create gate settings for every outlet in a rating group at WTYT2.
-    gate_settings.createGateSettings("SWF", "WTYT2", start_cal.getTime(), end_cal.getTime())
+    gate_settings.createGateSettings("SWF", "WTYT2", start_date, end_date)
 
 
 if __name__ == "__main__":
diff --git a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalc.py b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalc.py
index 8e4df61..6909d44 100644
--- a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalc.py
+++ b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalc.py
@@ -2,19 +2,19 @@
 
 
 def calculate_inflow(registry):
-    # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar, TimeZone
+    from datetime import datetime, timezone
+    from zoneinfo import ZoneInfo
+
 
     # this gets a scriptable Pool Percent object
     inflow_calc = registry.getCalculation(1.0, "Inflow")
 
-    # Time zone must be set because the Solaris time zone is UTC
-    time_zone = TimeZone.getTimeZone("US/Central")
-    # configure the start calendar
-    start_cal = Calendar.getInstance(time_zone)
-    start_cal.clear()
-    start_cal.set(Calendar.YEAR, 2015)
-    start_cal.set(Calendar.MONTH, 4)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    # Java's Calendar.MONTH was 0-indexed (4 == May); datetime.month is
+    # 1-indexed, so we use 5 here for the same date.
+    start_date = (datetime(2015, 5, 1, tzinfo=central)).astimezone(timezone.utc)
 
     # inflow_calc contains 4 callable methods:
     # autoAdjust
@@ -32,7 +32,7 @@ def calculate_inflow(registry):
     #   freezeRain
 
     # This autoBalances ALAT2
-    inflow_calc.autoAdjust("SWF", "ALAT2", start_cal.getTime(), False, False)
+    inflow_calc.autoAdjust("SWF", "ALAT2", start_date, False, False)
 
 
 if __name__ == "__main__":
diff --git a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcAutoAdjust.py b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcAutoAdjust.py
index 5825fa1..61ee5ef 100644
--- a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcAutoAdjust.py
+++ b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcAutoAdjust.py
@@ -2,17 +2,19 @@
 
 
 def calculate_inflow(registry):
-    # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar, TimeZone
+    from datetime import datetime, timezone
+    from zoneinfo import ZoneInfo
+
 
     # this gets a ScriptableInflow instance.
     inflow_calc = registry.getCalculation(1.0, "Inflow")
 
-    # configure the start calendar
-    start_cal = Calendar.getInstance(TimeZone.getTimeZone("US/Central"))
-    start_cal.clear()
-    start_cal.set(Calendar.YEAR, 2018)
-    start_cal.set(Calendar.MONTH, 6)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    # Java's Calendar.MONTH was 0-indexed (6 == July); datetime.month is
+    # 1-indexed, so we use 7 here for the same date.
+    start_date = (datetime(2018, 7, 1, tzinfo=central)).astimezone(timezone.utc)
 
     # inflow_calc contains 4 callable methods:
     # autoAdjust
@@ -30,7 +32,7 @@ def calculate_inflow(registry):
     #   freezeRain
 
     # This autoBalances ALAT2
-    inflow_calc.autoAdjust("SWF", "ALAT2", start_cal.getTime(), False, False)
+    inflow_calc.autoAdjust("SWF", "ALAT2", start_date, False, False)
 
 
 if __name__ == "__main__":
diff --git a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcBalanceAll.py b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcBalanceAll.py
index a9cb225..a9197cd 100644
--- a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcBalanceAll.py
+++ b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcBalanceAll.py
@@ -2,17 +2,19 @@
 
 
 def calculate_inflow(registry):
-    # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar, TimeZone
+    from datetime import datetime, timezone
+    from zoneinfo import ZoneInfo
+
 
     # this gets a ScriptableInflow instance.
     inflow_calc = registry.getCalculation(1.0, "Inflow")
 
-    # configure the start calendar
-    start_cal = Calendar.getInstance(TimeZone.getTimeZone("US/Central"))
-    start_cal.clear()
-    start_cal.set(Calendar.YEAR, 2018)
-    start_cal.set(Calendar.MONTH, 7)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    # Java's Calendar.MONTH was 0-indexed (7 == August); datetime.month is
+    # 1-indexed, so we use 8 here for the same date.
+    start_date = (datetime(2018, 8, 1, tzinfo=central)).astimezone(timezone.utc)
 
     # inflow_calc contains 4 callable methods:
     # autoAdjust
@@ -30,7 +32,7 @@ def calculate_inflow(registry):
     #   freezeRain
 
     # This autoBalances ALAT2
-    inflow_calc.balanceAll("SWF", "ALAT2", start_cal.getTime())
+    inflow_calc.balanceAll("SWF", "ALAT2", start_date)
 
 
 if __name__ == "__main__":
diff --git a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcClone.py b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcClone.py
index d3590d5..32791aa 100644
--- a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcClone.py
+++ b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcClone.py
@@ -2,17 +2,19 @@
 
 
 def calculate_inflow(registry):
-    # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar, TimeZone
+    from datetime import datetime, timezone
+    from zoneinfo import ZoneInfo
+
 
     # this gets a ScriptableInflow instance.
     inflow_calc = registry.getCalculation(1.0, "Inflow")
 
-    # configure the start calendar
-    start_cal = Calendar.getInstance(TimeZone.getTimeZone("US/Central"))
-    start_cal.clear()
-    start_cal.set(Calendar.YEAR, 2018)
-    start_cal.set(Calendar.MONTH, 7)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    # Java's Calendar.MONTH was 0-indexed (7 == August); datetime.month is
+    # 1-indexed, so we use 8 here for the same date.
+    start_date = (datetime(2018, 8, 1, tzinfo=central)).astimezone(timezone.utc)
 
     # inflow_calc contains 4 callable methods:
     # autoAdjust
@@ -30,7 +32,7 @@ def calculate_inflow(registry):
     #   freezeRain
 
     # This autoBalances ALAT2
-    inflow_calc.cloneInflows("SWF", "ALAT2", start_cal.getTime())
+    inflow_calc.cloneInflows("SWF", "ALAT2", start_date)
 
 
 if __name__ == "__main__":
diff --git a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcComputeEvapAsFlow.py b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcComputeEvapAsFlow.py
index 8f5bce3..e32c8e5 100644
--- a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcComputeEvapAsFlow.py
+++ b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcComputeEvapAsFlow.py
@@ -2,26 +2,23 @@
 
 
 def calculate_inflow(registry):
-    # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar, TimeZone
+    from datetime import datetime, timezone
+    from zoneinfo import ZoneInfo
+
 
     # this gets a ScriptableInflow instance.
     inflow_calc = registry.getCalculation(1.0, "Inflow")
 
-    # configure the start calendar
-    start_cal = Calendar.getInstance(TimeZone.getTimeZone("US/Central"))
-    start_cal.clear()
-    start_cal.set(Calendar.YEAR, 2018)
-    start_cal.set(Calendar.MONTH, 4)
-
-    end_cal = Calendar.getInstance(TimeZone.getTimeZone("US/Central"))
-    end_cal.clear()
-    end_cal.set(Calendar.YEAR, 2018)
-    end_cal.set(Calendar.MONTH, 4)
-    end_cal.set(Calendar.DAY_OF_MONTH, 4)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    # Java's Calendar.MONTH was 0-indexed (4 == May); datetime.month is
+    # 1-indexed, so we use 5 here for the same date.
+    start_date = (datetime(2018, 5, 1, tzinfo=central)).astimezone(timezone.utc)
+    end_date = (datetime(2018, 5, 4, tzinfo=central)).astimezone(timezone.utc)
 
     # This computes and saves evap as flow for EUFA in May 2018
-    inflow_calc.computeEvapAsFlow("SWT", "EUFA", start_cal.getTime(), end_cal.getTime())
+    inflow_calc.computeEvapAsFlow("SWT", "EUFA", start_date, end_date)
 
 
 if __name__ == "__main__":
diff --git a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcComputedInflow.py b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcComputedInflow.py
index 591325f..a977571 100644
--- a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcComputedInflow.py
+++ b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcComputedInflow.py
@@ -2,26 +2,23 @@
 
 
 def calculate_inflow(registry):
-    # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar, TimeZone
+    from datetime import datetime, timezone
+    from zoneinfo import ZoneInfo
+
 
     # this gets a ScriptableInflow instance.
     inflow_calc = registry.getCalculation(1.0, "Inflow")
 
-    # configure the start calendar
-    start_cal = Calendar.getInstance(TimeZone.getTimeZone("US/Central"))
-    start_cal.clear()
-    start_cal.set(Calendar.YEAR, 2018)
-    start_cal.set(Calendar.MONTH, 4)
-
-    end_cal = Calendar.getInstance(TimeZone.getTimeZone("US/Central"))
-    end_cal.clear()
-    end_cal.set(Calendar.YEAR, 2018)
-    end_cal.set(Calendar.MONTH, 4)
-    end_cal.set(Calendar.DAY_OF_MONTH, 4)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    # Java's Calendar.MONTH was 0-indexed (4 == May); datetime.month is
+    # 1-indexed, so we use 5 here for the same date.
+    start_date = (datetime(2018, 5, 1, tzinfo=central)).astimezone(timezone.utc)
+    end_date = (datetime(2018, 5, 4, tzinfo=central)).astimezone(timezone.utc)
 
     # This computes and saves inflow for EUFA in May 2018 given the computation options set above
-    inflow_calc.computeInflow("SWT", "EUFA", start_cal.getTime(), end_cal.getTime())
+    inflow_calc.computeInflow("SWT", "EUFA", start_date, end_date)
 
 
 if __name__ == "__main__":
diff --git a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcZeroNegative.py b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcZeroNegative.py
index b0e85ad..4f2e8d9 100644
--- a/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcZeroNegative.py
+++ b/regi-headless/src/test/resources/usace/rowcps/headless/examples/InflowCalcZeroNegative.py
@@ -2,17 +2,19 @@
 
 
 def calculate_inflow(registry):
-    # Java imports must happen after regi_session starts the JVM.
-    from java.util import Calendar, TimeZone
+    from datetime import datetime, timezone
+    from zoneinfo import ZoneInfo
+
 
     # this gets a ScriptableInflow instance.
     inflow_calc = registry.getCalculation(1.0, "Inflow")
 
-    # configure the start calendar
-    start_cal = Calendar.getInstance(TimeZone.getTimeZone("US/Central"))
-    start_cal.clear()
-    start_cal.set(Calendar.YEAR, 2018)
-    start_cal.set(Calendar.MONTH, 7)
+    # Time zone must be set explicitly because the JVM's default timezone is
+    # UTC, not the district's local time.
+    central = ZoneInfo("America/Chicago")
+    # Java's Calendar.MONTH was 0-indexed (7 == August); datetime.month is
+    # 1-indexed, so we use 8 here for the same date.
+    start_date = (datetime(2018, 8, 1, tzinfo=central)).astimezone(timezone.utc)
 
     # inflow_calc contains 4 callable methods:
     # autoAdjust
@@ -30,7 +32,7 @@ def calculate_inflow(registry):
     #   freezeRain
 
     # This autoBalances ALAT2
-    inflow_calc.zeroNegatives("SWF", "ALAT2", start_cal.getTime())
+    inflow_calc.zeroNegatives("SWF", "ALAT2", start_date)
 
 
 if __name__ == "__main__":