Hideaway Beach, the adults-only end
Since January 2024 the island has had a fenced-off adults-only zone, Hideaway Beach, for passengers 18 and over (21 to drink). It has its own beach, a pool with a swim-up bar and a DJ, seven places to eat and drink, and a heated infinity plunge pool open only to people renting the Hideout cabanas. Entry is a separate day pass - launch pricing ran $39 to $89 depending on the season - and daily occupancy is capped at 1,800 guests, which is a small slice of what one large ship carries.
A drinks package bought on board carries over to the island, Hideaway included. Coco Beach Club is a separate pass again.
Changing your mind costs nothing until the day before
Royal Caribbean refunds Hideaway day passes and cabana rentals if you cancel at least 24 hours before the ship's CocoCay call. That makes it reasonable to book early, while there is still space under the cap, and drop it once the forecast for your date is in - Aug-Oct calls are the ones most often swapped out for weather.
Sources: royalcaribbean.com, travelmarketreport.com