[remindme] Someone without a valid timezone gets an error when trying to use 20:00

[RheingoldRiver]

Traceback (most recent call last):
  File "/home/bot/tsubaki/prod/lib/python3.8/site-packages/discord/ext/commands/bot.py", line 1232, in invoke
    await ctx.command.invoke(ctx)
  File "/home/bot/tsubaki/prod/lib/python3.8/site-packages/redbot/core/commands/commands.py", line 759, in invoke
    await super().invoke(ctx)
  File "/home/bot/tsubaki/prod/lib/python3.8/site-packages/discord/ext/commands/core.py", line 1543, in invoke
    await super().invoke(ctx)
  File "/home/bot/tsubaki/prod/lib/python3.8/site-packages/discord/ext/commands/core.py", line 931, in invoke
    await injected(*ctx.args, **ctx.kwargs)  # type: ignore
  File "/home/bot/tsubaki/prod/lib/python3.8/site-packages/discord/ext/commands/core.py", line 196, in wrapped
    raise CommandInvokeError(exc) from exc
discord.ext.commands.errors.CommandInvokeError: Command raised an exception: TypeError: cannot unpack non-iterable NoneType object