8-9 weeks. really though your can just watch your buds once the darken your harvest is ready check the lower buds too because if their not darkened they can yield out a bit more. so you can cut the top and let the rest flower until it darkens which over all will give you a larger yield
Like Mr2shim said, and AimAim...
If you are...lookin for a sign...
Look for Amber Trics... first sign...
Then you be fine...
when you have the higest % of cloudy/milky trics...
Good Luck....