Ah, when to harvest. Highly varied in my experience. Also highly subjective as to your objective in growing the evil weed. I grow more for seed now than bud, so I tend to harvest TOO LATE! OMG! Pull your hair out and run around the room! This cannot be! They are on the verge of rotting from botrytis here in the PNW by then, but you get more ripe and viable seeds that way. If I am growing for bud to smoke, I tend to harvest earlier. Earlier picked tends (but not always) to be a cleaner high and less of a stone in my experience. I would pick right when the pistils begin to turn colors and are mostly white, and the trichomes are still mostly clear. Riper more mature red pistil buds tend to be stonier with a heavier high. Also the terpene profile will change during the harvest window. Take into consideration, Cali-O. The original California Orange bred by Jerry Beisler (sorry, it was not Dave Watson) has a good amount of orange flavored terpenes rather early in ripening which peaks well before the THC peaks. So if you want the orange flavor weed you get less of the high. Later picked and you get more potent weed, but the terpenes fall off. For that reason this strain lost favor pretty early on in favor of other early California developed strains. I also noticed this the last time I grew GDP. The fake grape flavor declined as it ripened more. It also was very prone to PM later, so earlier picked was better for that strain. PM can be an issue with Colombian strains as well, as they ripen so late and are prone to PM in my experience (growing Colombian bag weed landraces).
Your mileage may vary though. Terpene profiles vary greatly (even between the same clones) with climate, temperatures, growing conditions and curing methods. As will the highs. Cannabinoids, terpenes and flavinoids all vary and change through the ripening cycle. Terpenes convert to terpenoids, terpenes and terpenoids can waft off in heat, and cannabinoids develop into other cannabinoids over the flowering time. For example, THC converts to CBN over time. CBDa and THCa convert to CBD and THC in the ripening and curing process. Also once they are knocked up by pollen the girls will change in profile. THC tends to drop when seeds develop. Energy is diverted from producing more flowers to ripening seeds.
Overall? I tend to cut buds once they form throughout the ripening process. Early, mid and late flowering. That way I get a reading of what they are like, start to finish. Then I sample and record the results, and if I grow that strain again for smoke, I harvest at my preferred time. O/w growing for seed, I wait as long as possible. Or I do both, cut earlier for smoke, and let the rest seed out. I smoke a lot of seeded weed. Unlike many claims that pollinating ruins bud results, it does not. I have some incredibly potent one hit weed full of ripe seeds right now. I crosses Grape Ape with Maui Waui Cherry Bomb and its the bomb. One hit and I am trashed for several hours. Its a high(er) CBC strain. It may also have the new ellusive THCp in it. THCp is said to be 30x more potent than plain Jane THC. I do not know anyone that tests for that cannabinoid though. Its one of the more recently discovered ones. I also dry sift most of my harvest into hash and that is always potent stuff even from the mildest bud.