On the first, you have 24 hours to leave BVI waters after you check out through Customs. Leaving the next morning is a piece of cake.

Going back to the BVI, may I suggest that there is no better time, and no better opportunity, to enjoy Leinster Bay/Waterlemon Cay than on that last night in USVI waters? Arrive there early to midafternoon to enjoy swim and snorkel. Next morning take the walk to Annaberg Sugar Plantation ruins, then the short sail to either Great Harbor, Jost or Sopers/West End to check back in. AFTER customs opens, and without hoping that maybe, baby, you can game that entry without getting caught doing something not quite legit.