Here's a simplified reproducer:

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("-u", "--utc", choices=["-1:00"])
args = parser.parse_args()

I assume this is related to argparse guessing if an argument is a negative number. See https://stackoverflow.com/questions/9025204/python-argparse-issue-with-optional-arguments-which-are-negative-numbers

From a suggestion there, note that
python test.py -u ' -1:00'
doesn't give the "expected one argument" error. I realize that doesn't solve your problem, but it does shed some light on the issue.

I suspect this can't be fixed without breaking other usages of argparse.