I would say at least a month.

You will see the buds swell up rather than get longer, and many of the little hairs (pistols) will turn brown.

The best way to tell if your buds are ready is to get a 30x magnifier and look at the tricomes (THC glands that will sparkle and frost the buds), when they get cloudy and begin to turn amber the bud is ready.

BTW, don't forget to dry and cure it properly for the best potency and smoke.