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.
I wasn’t looking too carefully at the actual dates you typed in, but the formula that I gave you is giving you the exact number of minutes that have elapsed between Date 1 and Date 2. Are you saying that you want it to completely ignore the dates altogether and just look at the times?