Depends on what time you leave the water park and whether or not you feel you have to stop by the hotel on your way. If you leave the water park at 12:30pm and go directly to MK, it's plenty of time. If you leave the water park at 1pm and want to stop at the resort first, it's not.
I would be nervous to do that simply b/c I always lose all track of time at the water parks...just like at the beach, what seems like 30 mins. is really an hour. But if you're not dealing with kids, then just maybe...
Dpends on time of day. If there are no lines, you can do a waterpark in a few hours. Bring a change of clothes, and be at the busstop to mk by 1 or so.
I've done a water park to a PS at 5:30p.m. We left the water park at 1 pm. It gave us enough time to get to the hotel, clean up, and relax. It also gave us enough time to enjoy the water park.