What time is your flight scheduled to depart? The shuttles are scheduled based on YOUR flight schedule. If you have a flight at midnight, they will have a shuttle ready to take you back to MoBay at around 7:00 p.m.
We have found that they are very strict about asking you to check out of your room on your day of departure. However, they will store your luggage for you, and you can roam the grounds until you are ready to leave for Mobay. If necessary, you can shower and change in the locker rooms located across the street in the fitness center. We checked out on our last trip, and had time to walk the beach and have lunch prior to catching a cab to Negril airport (we took TimAir on this trip, so we were able to have a later departure time).
Keep in mind that the shuttles have been leaving between 4-5 hours prior to the scheduled departure times. So I guess theoretically you could hang around the resort all afternoon after checkout, but the reality is that you need a big chunk of time to get back to Mobay.
I haven't booked flights yet. Typically the latest flight home for us is 2PM, so our time at the resort on day of checkout is very short. I was considering booking a flight on the day after check out, staying at the resort as long as possible and then staying in MoBay to catch an early flight the next day. That would be a waste if we had to leave shortly after checkout.