We did the wave runner excursion at Ocean Cay in January. We received the tickets in our stateroom the day before with an assigned time. Depending on how many people have booked, you might be able to request a different time.
Be aware, this is a tour, you are not able to go where you please but are in a group with a leader who you follow.
We were lucky as there were only three couples in our group and it was great, but the group before us had about ten which I’m thinking led to a lot of waiting around.