JDC

We are debating booking an excursion in Grand Cayman or simply using their public transport and/or taxis to visit the same places. A couple of people have suggested to me that Grand Cayman is very safe and easy to navigate without a pre booked excursion. They have some of the options we like listed as excursions but they seem very rushed at 3.5 hours when our ship is scheduled to be in port for 10 hours. Not looking to push it, but I think all of the excursions would be much more relaxed and enjoyable with the freedom not being with the official excursion group would allow. FYI we are looking at the dolphin encounter, turtle center, or possible the manta ray. We think we could do one or two of the above and stop of for an hour at the beach and still leave for the ship by 4 for an on board time of 6. Does anyone here have experience going it alone? If you book an excursion and decide to stay longer or explore something else can you ditch your group?