If you were sailing out of Ft. Lauderdale I would say it would be calling it close--but sailing out of Miami is way too close! You might luck out and get on an earlier flight if your on standby, but what if you don't? If it were me, I would first call the airline and talk to a supervisor; tell your story, and see if they can help with the change fee. Book the day before the cruise even if you have to pay the change fee. Better safe than sorry...