I would say the pistils are what you use as the sign to start checking trichomes. When they stop reaching out is when I would say you start checking trichomes on buds, not on leaves. Some more experienced growers don't even check them at all as they feel they can tell just by the look of the plant however I am not there, I still use the trichomes to determine when to chop. Plants can ripen more on one cola than the next, this is why some harvest in stages. To me his main cola looks ready and the smaller ones may have some more time. Waiting for clearer pics.