When you arrive early, can you use magiquest, or go to the arcade?

Yes, you can. You can also use the water park from noon time.

Early water park access starts at 1pm, but you can go even earlier if you want to MagiQuest or play in the arcade. The only time they check for your guest bracelet is going into the water park.

Yes, you can also go into the Waterpark prior to your room's check in time. They'll hold your luggage for you if needed.