Thanks to all who contributed to this thread.
Last update after we made it home:
7:30 Sensation ferry VG to RT: on time, ca. 30 PAX, 10$pp (senior)
8:30 Aquatic Rentals RT to RHK: pre-booking did not help, had to queue in front of booth, very slow process, you can save the 10$ internet fee, took 30min, AR staff very helpful, captain did not leave dock before last PAX came on board (boat left 8:45 actually), security on 'international' side of ferry terminal is pathetic, hand luggage undergoes a lot of scrutiny
9:30 arrival Cruz Bay/St Thomas: 50 PAX queueing through customs building /w luggage, 3 of 4 booths open, 30min delay, photos and fingerprints being taken
10:20 arrival RHK, 'bus' in front of ferry terminal waits until 8 PAX on board, if you are last off the ferry you have to wait, we finally left /w 6 PAX after offering 30$ pp (nominal fare 23$ pp)
10:45 arrival STT departures, 2:40 h before our Delta flight, other folks in the bus made their Miami flight w/ less the 90min to go
Check-in at Delta took less than 10min (due to our early arrival and only luggage tags are applied)
However, STT airport is a total mess:
* You have to undergo US immigration a 2nd time, having your photo taken a 2nd time, carrying ALL your luggage
* Only 2 security lines were open
* The gate area is VERY crowded, 1 windowless restaurant /w tables, paid almost 50$ for some kind of BF
It was a Thursday, I wonder how it would have been on a WE...