Bob, you should be fine. A few weeks ago, our crew had a 2:30 pm flight out of STT on a Thursday. They were taking the Noon ferry from Road Town. TMM will wanted them in a taxi by 10:00 am to get to the ferry. We were staying on so the debriefing wasn't a time crunch for us.
Last March, TMM required that we spend the last night in the marina in order to be debriefed and in a taxi by 10:00 am.
Also, note the fuel dock in Road Town doesn't open till 7:30 am so you'll have to allow for time for that.
Hope that helps!