Another thing to remember is that depending on the ship, ship's time and local time can be different! Some ships stay on ship's time the whole cruise, other's change time as they go from time zone to time zone. That can make it even more confusing!
As for the dolphin swim - we booked the last swim of the day thinking we had three hours total to do the swim and get back to the ship. Well, we stayed on ship's time not local time which cut it to two hours. There were 15 of us (8 did the swim and the rest watched and recorded it for us) and the last of the group got back to the ship 10 minutes before sailaway...NEVER AGAIN!!!!