I do not know how long it takes to get to that cave sight, but it takes acouple of hours to get to Belize City... much longer on the local bus. First Class bus is definately worth the extra couple of dollars. Last flights to San Pedro from Belize Municipal are around 6PM. Last water taxi's I believe around 5PM. Do not run late and get stuck in Belize City unless you can stay at the Princess Hotel or maybe the St George Radisson. Belize City does have "street crime" at night.