The procedures and time involved for your group, particularly as all are US citizens, is not too great; particularly when offset against a 10 day cruise. I will assume that your charter company will allow a trip across to the USVI. You will need your boat papers from them and then will need to clear out in BVI; Road harbour is a bit of a hassle as you need to get to the Ferry Terminal and they don't have a dinghy
dock. The West End, being within sight of the USVI is the logical choice but you can also check out of Jost Van Dyke or Virgin Gorda. I would recommend checking in to the USA on St. John, there is a draft restricted temporary anchoring area in Cruz Bay (too shallow for my deep draft) or you can take a mooring ball somewhat north of Cruz Bay in Caneel Bay and dinghy
in to Customs & Immigration from there.
I would guesstimate about 30-60 minutes to check out at the West End (assuming you time it well and don't check out when a ferry arrives) and about the same time in the US. I normally need to ask for checkout papers in the USVI (they aren't issued as a matter of course) but when travelling to BVI they will let you check in without checkout papers. I am not sure what the checkout procedure for you would be, as a non US-citizen I need to go into the offices but in your case a telephone call might suffice. Checkin into the BVI will take about 60 minutes.
I went to St. Johns the first time to pick up and later to drop off a friend. After dropping her off I had intended on sailing back the BVI but ended up spending a week in and around St. Johns, mostly moored in Caneel Bay, and loved it. The food at the campsite is worth the 200+ steps that you have to surmount and those steps help to work up an appetite as well.