Just read a post regarding cutting it too close to get back to the ship - we have reserved the fatcat catamaran in Calica/Playa del Carmen - it is scheduled to return to the dock at 2:30 in Puerto Aventuras and our ship leaves at 4:00!! Will we have enough time to get back to the ship?
As long as they stay on schedule you should be fine. Puerto Aventuras is not that far from Calica, maybe 15-20 minutes if memory serves me correctly, should be a $10 cab ride. The Omni Resort there is really nice and they treat you very well if you want to go a little early and have a cocktail at their beach bar. There also have the Dolphin Experience there as well. Its neat to see. There are a lot of cool shops and restaurants surrounding the resort. The Omni even gave us a ride back to the hotel for $12 so we didn't have to worry about trying to find a cab inside the gated resort area.
As long as you have 30 minutes to spare before last boarding you will be fine, my sister in law, husband and kids were on the same trip last month and had no problems with the return or meeting time. You should perhaps ask the Western excursion people at http://belizecruiseexcursions.com they will be able to tell you if it is possible or not, I am sure they know much better than I do (or my family for that matter