I have to second the checkin / checkout in Jolly harbour rather then Falmouth/English - if you are in luck you can dock
right in front of the 3 little offices at the "Q" dock
otherwise take a mooring
ball or anchor out and dinghy
You didn't specify what sort of a boat you'll have or if you wish to use your iron genny - that will make a big difference in estimating your time to Antigua on that run. I have done Marigot -> anchorage off Nevis
("Q" flagged for the night), then departed at dawn for English Harbour twice but only when the wind has a significant northerly component, more than ENE. [with little swell one can better the angle by going north of Nevis, Hud3 can give better advice than I on that passage].
St. Barths to Jolly Harbour is about 75nm. Even without a GPS
you will have some island on your horizon for the whole trip (St. Barths, St. Kitts, Nevis, Montserrat) to give you orientation and usually you'll have a large area of cumulus forming over Antigua during the day to show you where the island is.
With typical trades you'll have the relative wind on your port beam and will make good time, if you turn on the engine
you can easily plan on getting hull speed
and can compute your departure time from St. Barths so that you get in to Jolly harbour or English/Falmouth at 9 (no use getting there earlier since chances are that nobody will be at customs/immigration). If you anchor at the edge of the mooring
field in St. Barths then departing in the dark should pose no problems at all.
There will be a couple of ferries on the same route
, but the heavy iron traffic route is north of St. Martin heading SW. The only real traffic will be other sailboats and big power yachts going from Antigua to St. Barths/St. Martin.