Yes we know it's a long day - leaving at 6am should get us there by 10-11 am, gives us plenty of time to do what we want and leave by 3 or 4 to get back by 7-8pm
Make sure you take traffic in Kingston into consideration. It took us at least 1 hour to go from Port Royal to the Marley museum and that was with a driver that knew Kingston. Drivers will say they know Kingston but what they mean is they know how to get there.