You can take one of many day sails from STT to JVD and some other islands such as Virgin Gorda, Norman,...all in same day and have them drop you off on STJ at Cruz Bay on the way back. From there, you will take a taxi to Maho Bay. You might want to look into a cottage on the beach at Cinnamon Bay, for the same price. Next day, taxi back to Cruz Bay for ferry to Charlotte Amalie or ferry to Red Hook and taxi to CA.

HOWEVER, if it's your first time to USVI/BVI, I would strongly recommend that you rent a car from CA, drive to Red Hook, take the car barge over to STJ, explore and enjoy the many beautiful beaches over that island. Spend every seconds of your 1.5 day there.

Have fun.

You can take the ferry from Red Hook, STT, to Jost. It stops in STJ going and coming. Only ferry back is at 3 from Jost to STJ and then to STT. Check schedule above. Jost ,White Bay, is awesome but the trip will consume much of your day. with only 1.5 days you may be better off sticking to STJ. There are many a fabulous beach to be had. Easily use up your time here. Check the ferry schedule above and don't forget the travel times involved to and from the ferry dock. it's 30 - 45 min, on a fairly good day, from the airport to red hook. Ferry wait time then 30 min. to STJ. Don't over stuff your day. Relax and enjoy these awesome islands.

As others have mentioned, you really are trying to pack a lot into 1.5 days. I can understand wanting to see as much as you can in the time given and while it is possible you really should take some time to "smell the roses" while there (not that you'll find many roses). Better to take it in, see what the possibilities are and make plans to return. Racing from island to island negates the slow pace benefits they have to offer.