I think you'd want to book for the night your in Nassau...But your room may not be ready for you until early afternoon. I think when this happen...your able to go to Atlantis and do your thing over there...you just can't get into your room until it's ready...If you did it the other way...you'd have to be out of the room by the check out time...which could be anywhere between 10am and noon....So doing it that way your room would be ready for you in the morning when you arrived in Nassau....but you couldn't use it later in the day...and you'd have to have all your things out by check out...not sure if your able to continue using the faclities at Atlantis after your check out time...anyway's I think you'd want it for the night OF...not the night before. JMO.