Personally speaking, I wouldn't bother with St. John for such a short visit. Clearing customs isn't that big a deal, but it does take time and you have to do it 3 times. Out of the BVI, in at Cruz Bay ST. John and back in to the BVI. If it was me, I'd opt for either JVD for day 2 as well seeing that you'll only have the afternoon there day 1 - you could also fit in some time at CGB. Or just move everything else up a day too. Anytime we go to St. John, it is for at least 2 nights.

As far as getting off the dock by 11. It is possible. We've done it. We are also owners with Moorings though so our check out process is very quick. I typically know the boat we're on, where everything is and have gone through it before we brief. Only time we've been later is if we'd had issues with something missing or broken and had to wait.

So, if you are able to do the chart briefing (if required) the night before and either go over the boat thoroughly yourself and either do the boat briefing the night before or as early as they can do it, then you'd probably have a good shot at getting out by 11. Although this also depends a lot on the charter company.