In my opinion, it's ready to pull once they are all milky (right now) and you're just starting to see some mature amber ones. Some folks wait for there to be more amber trichome heads. From what I've heard, it's more personal preference on how "sleepy" you want the effects to be from the continued degradation of THC, other cannabinoids, and terpenes into whatever compounds are responsible for that (purportedly related to THC - CBN conversion but scientifically rigorous evidence of that has not yet been seen).
