It depends, usually between 8-12 weeks. Sativa's take the longest. Nevertheless, if you are growing outdoors you want to be chopping in mid October, maybe later. If you are growing indoors, 12/12 for 8-12 weeks. You want fat buds remember so dont be tempted to chop sooner than when they are ready. You would have waited all that time after all. Dont forget to flush.