Your ship calls at Road Town cruise pier. A private boat takes you to Jost Van Dyke in about 18 min and brings you back with margin on the all-aboard time — not on a tour operator's schedule.
Shore excursions leave in groups and come back late; the public ferry does not wait for a cruise passenger, and missing the all-aboard at Tortola means catching up with the ship at your own cost.
A private boat departs on your time, covers the 14 km in about 18 min, and the return is planned backwards from your all-aboard.