My DW and I, and friends, booked the 11:15 tour originally. Before we got to the island, we had discussed that we'd like to go on the earlier excursion to Stingray City which would allow us more time in the afternoon to enjoy 7 mile beach on Grand Cayman.
When we disembarked, we walked to Captain Marvin's office (not too far from the tender area) and inquired. The earlier trip was booked solid. We asked them for options and we were offered a different trip (Coral Gardens, Barrier Reef and Stingray City) which left about 45 minutes later. The trip was $5 or $6 more per person, but the time savings to leave earlier and get back earlier was well worth it. We absolutely loved it! The boat we were on was full, but not uncomfortable at all, the crew was nice and helpful too.
My word of advice is to take the earlier trip to save more beach or shopping time in the afternoon. We asked the van driver from Captain Marvins drop us off at the Holiday Inn on 7 mile beach on our way back. We spent a few restful hours there and caught a taxi back to the ship.
Happy cruising!!
Howard