I think he is leaving Tortola catch a flight out of STT at 12:55. He will need to check the boat in and take the ferry to St. Thomas and get to the airport.

Personally, I think that is too much of a risk. You need to take the first ferry out of Tortola, 7AM, the next one doesn't leave until 9:30/10:00. That would be cutting it way to close for my comfort.