As a matter of law, if you are forbidden to leave, you are supposed to get paid. If it's impractical but technically allowed for you to leave, it can be a grey area but it only usually falls on the employer if they are the ones putting up a roadblock that stop syou (for example requiring you to change out of uniform)

I don't really have a problem with that honestly. If I'm frree to walk out the door and not suffer any negative employment consequences I don't see why I'd get paid for that time.