No, it wouldn't leave you enough time to do an excursion on St. Thomas and then head to St. John. You need to take a ferry to St. John and they only leave every hour on the hour. The ride from the dock to the ferry is approx 20 minutes, with the ferry being 20 minutes long. It is possible it could take you over an hour to get to St. John, and then it's approx another 10 minute cab ride to Trunk Bay. Then you have to reverse everything and get back to the ship by 4PM, to ensure you won't miss the ship!! The latest ferry I recommend people being on, since traffic on St. Thomas can get horrible when a lot of ships are in port, is the 2PM ferry from St. John. It gets back into Red Hook around 2:30, so with even tons of traffic (it has taken me 45 minutes to get from Red Hook to the dock area before) you'll have plenty of time to get on the ship. The 3PM ferry would be cutting it close too IMO. If you have a morning excursion, you probably wouldn't get over to ST. JOhn before 1PM, leaving you almost no time to see anything. If you really want to go to St. John, you'd have to cancel your excursion. We travel to St. John frequently (usually once a year) and it is truly a beautiful place!!