It's all about the trichomes! If you prefer that "couchlock" stone from Indica genes OR are going for CBD content, then run them till the triches are around 5% to 10% or 15% amber colored. Main rule of thumb, plant is RIPE when all (or >90%) of the triches are a Milky White. If you prefer to get the more of a "Trippiness" of Sativa genes out of ur smoke, thengo a bit early (70%-80% Milky white, the rest Clear).
If you don't have 10x jewlers Loupe or a cheap hand held microscope (you can even get USB conected microscopes fairly cheap...), then do a blackout of the grow area and stand 15 to 20 feet away (as far as you can, and shine a flashlight on it and if it glistens, looking like a freashly Glazed Donut, then the Milky triches are pretty much ready (this is word of mouth, but from and outdoor guerrilla grower that a friend knows)
Rule of thumb:
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Ripe=THIS:
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Couchlock=THIS: (or maybe even MORE of a concentration, but not to much...once the tirches start turning amber, THC starts degrading, as the first illustration says)
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