CBD-level peak

There are ofc genetical variation but trichomes are susceptible to excess light and heat which can accelerate the degredation. So make sure you are lowering dli and temps for last week or two. Ideal world you want everything filled 90% milky and 10% amber. Sometimes if you run too hot you can see more like 40% clear, 40% milky 20% amber. We don't want any degredation to happen until everything is milky first you see.

THC degrades to CBN. CBD degrades to THC, then to CBN but never to CBN directly.

Basically, more brown, more CBD..........but.......there is a limit. Once the plant reaches peak maturity, leaving it longer to achieve more degradation in the hope of increasing CBD levels will not work. CBD plants are bred for CBD production, obviously, so you still want to harvest a plant in the prime of its life, as once past the peak, declining health means all cannabinoids break down into useless compounds with low quality effects. My advice would be to harvest once the plant is fully mature with 100% brown pistils/hairs and not stress over amber trichome percentages, as the trichomes will be full of CBD anyhow and leaving them longer or harvesting a bit earlier will affect that concentration by only a tiny, tiny amount. Harvest happy and healthy mature plants and don't let it over ripen otherwise the CBD will break down just like THC degrades if left too long.