The earliest I checked in was on our last stay and that was 11:30am and our room was ready so we were allowed in. I wasn't expecting the room to be ready that early, I just wanted to get my parking permit and head to the parks so it was a nice surprise. If the room is ready, they'll let you in, if not you can still pre-check in, stow your luggage and get a parking permit if you need one. They will tell you to come back after 4 but I've stayed at Hojo's 6 times in the last year and only once did we actually have to wait till after 4pm.