I think it depends on how flexible you are and how full the resort is. Also, some luck of the draw. If the party in the room assigned to you has checked out and mousekeeping is done, they will give you your room. However, if you are requesting a certain building/floor/room, etc. you may have to be patient waiting for it to be ready. Also, if the resort is full...it will take longer to clear out.
But, you can "check in" at the desk, leave your stuff with bell services, get your tix if you need and head off to start your day. You can also use the pool, your room charges, etc...even if your actual room is not ready. At the BW last year we left our cell phone # and they called when our room was ready.