Our observations, life guards leave at 2200, people swim up to and past MN as long as they are quiet. If they make a ruckus they are advised to leave the pool area. Always request a room away from the pool to avoid these disturbances. 
When we were at POP coming back from MK after MN there we 8 or 10 folks in the main pool quietly enjoying...can't speak to the other pools, but again if you are quiet I don't know that they kick you out at any given time.