I don't know about the Dolphin specifically but I usually check in early at DW ( as early as 7:30 am). If they have a room ready, they will give it to you. If they don't, you will need to wait for the room to which you have been assigned. I'm sure you can store your luggage with bell services and go to the parks or the pool. You'll find a lot to do if you can't get into your room right away. The Dolphin is in a great location.