Are you on a cat or a mono? What size? I ask because it might be important depending on the conditions you see in January. Frequently that time of year you can see some stronger winds from a ENE, NE or nearly straight north.
If on a cat I would head east from Culebra to the lee side of St Thomas. Most charter cats don't go to weather well. You will most likely be motoring or motor sailing so why not spend the least amount of time in rough waters? From Culebra to STT (to buy water if you wish) is about 18 miles or around 3hrs. Stop for lunch and in another couple of hours you are on a mooring in calm water on St John. I assume you are going to Vieques for the Biobay which means you would be leaving from around Esperanza. From there to St Thomas one is traveling about 32 miles. If there is any north in the wind at all, even a mono won't be able to lay STT. If winds are straight east you may be able to get there on one tack depending on sea state, vessel and sailing skill. Assuming you sail well and are doing 6kts beating you have about 5hrs ahead of you. I've made the trip from Culebra and Vieques back to St Thomas many times on everything from a 31' mono to a 46' cat. My preference is the short run from Culebra unless the sea is pretty flat, which is unlikely in January.
Enjoy your trip