Convert dates to julian day number in astropy?
The accepted string formats for date-hms are:

Format  Class    Example argument

fits    TimeFITS    ‘2000-01-01T00:00:00.000’
iso     TimeISO     ‘2000-01-01 00:00:00.000’
isot    TimeISOT    ‘2000-01-01T00:00:00.000’


https://docs.astropy.org/en/stable/time/index.html

You can either change one of these, or you can define your own format by deriving a class for the format from the TimeFormat class.
https://docs.astropy.org/en/stable/api/astropy.time.TimeFormat.html#astropy.time.TimeFormat