I do the Moorings to the 11:00 ferry all the time. Set your cab pickup for 9:45. Once you arrive in STT stow your bags at the customs exit and walk into town for a nice lunch. We like the green house. Shop a bit and be back about 2:30 to head to the airport. As an alternative you can have the cab drop you at the Emerald Beach resort and enjoy lunch there. Arrange the pickup for 2:45 if you go that route. I use Stanley from Love cab and he handles our bags throughout either option so painless.
Love Cab
340 473 6344