Depends on the maturity of the plant, plant strain, stress. by 2 weeks you should see her starting to go into flower. unless you use "Bush-Master" then it will only take 4-7 days to make her go into flower. You don't really count the time it takes her to go into flower. ie. 8 week plant, 1-2 weeks to go into flower. so now you have 9-10 weeks she should be done, but that is just a rough gauge. use a pocket microscope, when you have about 75% amber trichromes, harvest. I've grown 16 week plants, you just have to be patient, and watch the trichromes, "When it's Done, It's Done"