I can't say for sure because I don't know your itinerary but I just got back from our cruise and when we had to go through immigration, it took forever because people were not showing up on time. We had a shore excursion at 8 and they didn't let us leave the ship till 9. We did this the day before departure because thats when we actually reentered the states, officially but if you have to go through immigration on your departure day, its up to your fellow passengers when you leave. They don't clear the ship till ALL have gone through.
That being said, if you don't have to worry about such things I think a noon flight gives you ample time for anything to happen. You never want to worry on vacation- why cut it so close?