I would be harvesting asap, once your plant has more than 95% brown pistils she is getting close to death, meaning THC is breaking down faster than it is being replaced, giving you sleepy herb rather than high/up herb, but if you prefer couch lock over head high, you can leave it until there are 100% brown pistils, but by then there is more CBD and less THC, which gives you the sleepy stone. If your prefer a clearer and more brain bending head high, in future, harvest when there are about 95% brown pistils, this is when there are peak THC levels and prime terpene levels too.
Hope this helps, Organoman.