+1

I've done it in far less than that from row 40-something on a 777.

Bottom line is, if the flight into MIA is on time, it's not at all a problem - 55 min is plenty of time. But since there's no guarantee it will actually be on time, if there's availability to make the switch, and you have the time to do it, it's a good idea. The last thing you want is to miss the start of your trip. Or stress for 3+ hours on your way to MIA that you'll miss the start of your trip.