Hi! When we did online ck in at Pop last October, I received a "your room is ready" text when we were on the Magical Express. It included our room # and when we got to the hotel we went straight to our room and dropped off our luggage and hit the parks!
Of course it all depends on the resort and there is no guarantee your room will be ready before you arrive. You can leave your luggage at guest services at AoA and go to the parks, your magic bands will be active, if your room is not ready. Have a fabulous trip!!