I have requested a late check out nearly every time we have stayed (mostly at HRH), and only once was I not granted it. Usually, they can accommodate an hour, but anything beyond that is going to cost an extra charge.
I have been denied any extra time at CBBR and Aventura. The reason given is the hotel is fully booked. I have used the locker room after swimming in the pool after checkout, but obviously luggage has to be held at bell services.