I've had great success using https://www.luggageloungemiami.com/ when killing time between disembarkation and a later flight, if going to the beach is of interest. I've used https://www.resortpass.com/ as well, and this option is really excellent if you have a very long time before a flight!
I've not stayed in the Haven, so I can't comment on how long they let you hang out before disembarking.