What is your option if you miss the flight from MIA to SXM? That is my first thought and so I then make my other flight plans based on that. I would rather be early and spend time at MIA then miss the flight. Note, probably not the last change your flights will see. I also have made it through MIA in less time, as well as other airports.

On the way home I don't sweat it as much if I miss a connector, but on the way down my island time is gold.