It should take you anywhere from 15 - 35 mins, depending on traffic to get to the beach. I think it's named Kaho beach, but I'm not sure. There is a bar there called "Baywatch" that you can perch at, drink a few Caribe's and gawk at the airliners.
The heavies come in late in the afternoon with the AA
ATR's, Cape Air's Cessnas and some of the US carriers coming in throughout the day.
It's not much of a beach though. I'm not sure how long you'll be at anchor, but the French side offers what I think are nicer (and nude) beaches, compared to the dutch end.
Be sure to stand directly under centerline and to wear goggles for the full effect of SXM