I don't know if it's still the case, but in the past, some Avis locations would pre-print the contract with a pick-up time 45 minutes after one's reserved time (so 12:45 pm for a 12:00 Noon reservation), and you would then have 24 hours and 29 minutes from 12:45 pm to return the car without incurring an additional charge. But I'm not sure whether that is offered when one selects their own vehicle rather than have Avis pre-assign one.