You will need to do the USVI portal twice. Once to enter and again to renter from the BVI. The antibody test makes that easy. You will have to do the BVI portal once for entry and that will require a covid test within 5 days of travel. If your flight is ontime 1.5 hours should be fine. Be aware however that the ferry companies will not refund your ticket and if you miss the 2:30 the later ferry might be at the 65 max capacity.