I have almost the same situation except I've already moved the whole charter over a day to give them more time and now they want to leave a day early. They need to take a ferry from Tortola to STT on Saturday so my plan is to put them off somewhere on Tortola (Beef, CGB or Sopers) as early as possible on Friday depending on where we are. We originally reserved rooms at the Mariners for Saturday so I just moved theirs back a day and they can taxi to the base leave their bags and sight see, hang out by the pool whatever. Then use their room and take the RT ferry the next morning. Meanwhile, we enjoy our Friday and a bit of Saturday before returning boat.