This really all depends on how you like to drink your beer. You could let it ferment for a week, put it in the keg, force carb at 30 psi and shake. You could be drinking green beer in a week and a day. I wouldn't suggest it though.
So it really depends on how long you leave it in the fermenter. If you leave it in the fermenter for three weeks or more, force carb at serving pressure for a week and you will be good to go. If you got it out of the fermenter early, you could load the keg with priming sugar and let it sit for at least 3 weeks which will let it condition and carb up.
There's many ways to skin a cat!