Atlantis website states the following: “Visit an Aquaventure Guest Services location with your valid room key for towels and Aquaventure wristbands.” This seems to imply that a guest has access for the number of days that they have a valid villa key, even if the stay is shorter than a week (ie 1-6 days). Upon emailing Atlantis I received the following response: "All stays at Atlantis, including Harborside Resort, include access to Aquaventure Water Park, The Dig and The Ruins Aquariums, The Marine Habitats, The Beaches, The Pools and the Casino."
DaveT