Thanks...Alamo offered me the chance to "check in" ahead of time, which I declined when the phone agent suggested the reserved time would be the one printed on the rental agreement. Instead, I delayed the pickup as long as possible, and the actual time out was the one printed. Then, 3 days later, I delayed the return as long as possible, returning the car at 72 hours +27 minutes after checkout. No penalty. Alamo has a 29 or 30 minute grace, which I would interpret as 29 minutes to be on the safe side.