Unless there is some unforeseen circumstance you can easily make an MIA flight by 10am. That should give you 2-3 hours to make your flight which is more than enough. Normally you get off the boat by approx 7:30a and it's about a 15 min taxi to MIA. As stated above, there is always the possibility of exceptions but they are not the norm, which is why they will be called exceptions. There are things you can do to help your cause such as carrying your own bags with you off of the boat, not having declarable items that have to be inspected by customs, checking in for flight online, private transfer to MIA, being TSA precheck to get through MIA faster and not traveling during peak times such as Christmas, Thanksgiving, Spring Break, etc.
On a side note, if you're flying American Airlines you have additional options that help eliminate any stress about making your flight. They have a "flat tire" policy. If you are less than 2 hours late for your flight, you can fly standby on the later flights for free or pay $75 pp for a guaranteed seat on a later flight. So for example, we are scheduled on a 9:30a flight back from our Magic cruise out of MIA in March. The next available flight was after 11:00a which was significantly more money and would have us waiting at the airport for hours. We took the cheaper 9:30a flight. If we miss the flight, no big deal. I'll just pay the $75 pp fee to be booked on the later flight and still save more money than I would have if I had booked the more expensive 11:00a to begin with. Everyone's different with personal preferences, this is just my 2 cents.
