Check in time is 3pm but if the room is ready prior to that they will let you go directly to your room. If it is not ready, you can leave your bags in your vehicle (some prefer not to do that just incase of theft) or you can leave your luggage with the bell staff. They will give you a ticket with a number and when your room is ready and you are checked in...you call the bell staff and they will bring it up within 15 minutes.
Yes, if you are there before 3pm you can swim. They have towels there you can use. There is a bathroom in the pool area where you could change. The one caution would be that I'm not sure if you can get in and out of your luggage to get things. But, you could pack a separate little bag that would have the swimming stuff in it so you didn't need anything in or out of your luggage, whether it is in your car or with the bell staff.
The same thing would happen when you check out. You could put the luggage in the car or have the bell staff come get your luggage and store it for you. Then you could go swim. Again, you might want to pack a separate beach bag with clothes in to change when you are done swimming. The towels wouldn't be a big deal because you get them there at the resort.
You might also ask for a late check out. They will often let you stay until 1pm depending on occupancy and housekeeping demands. That would give you some extra time. We've done this often. You need to ask when you check in. Sometimes they won't tell you until the day before you check out, though. That might be an option.
