we took a privat excursion to sandals during our Feb 05 cruise. Best time we had the entire cruise. you control when and where you go and return when you want. We have been on several RCCL sanctioned excursions that we got back just in the nick of time and didn't have time to visit the pier shops.
you do risk the posibility of missing the ship, however, our last cruise went to Costa Maya and several people were late arriving and the ship waited for them. So your call. I say GO, it's your vacation...enjoy it all you can.
Mariner of the Seas
with the boys