Just to help clarify, it's not actually a 48 hour requirement for the BVI, it's actually 2 days. So if you are ferrying to Tortola on a Friday, you can test anytime on Wednesday and use that test for your BVI entry. I'd suggest just taking your eMed.com test 2 days before your BVI entry and using that result for the USVI portal and the BVI entry.

No test required to board your flight in STT to get home.