k this is the esiest way to tell when to harvest regardless of schedual.
the hairs that come off of the buds should be clear or milky white. you should look over your whole plant every day or two and check if n e of them are starting to change to a orangish kind of color. as soon as u see that all of the hairs have turned from whte to orange, that second, that day, right then, chop that shit.
the resin is concentrated in those hairs and the tricombs, but once the plant reaches full flowering maturity (the hairs and tricombs change the color) the resen begins to deteriat. if u catch it right when u realize they have matured the thc rates (containd in resin) will be significantly higher than if u went stricktly on schedual alone.
peace and good growing!