Looks like you’ve got your date fields setup incorrectly. You’ll need to go into your customization options for your date fields, and make sure they’re both set to either GMT or not. They both need to be set to the exact same option. You can’t have one field set to GMT and the other field set to NON-GMT, because then you’re telling Airtable that your fields are in 2 different time zones.
If you’re ignoring the dates, then I would probably do it like this.
This formula will extract the time from the date fields as 24-hour military time, and then the math can be done on those military times:
IF( AND(Date2,Date1), DATETIME_DIFF( DATETIME_PARSE(TIMESTR(Date2),'HH:mm'), DATETIME_PARSE(TIMESTR(Date1),'HH:mm'), 'minutes' ) )