The only reliable way to tell when to harvest is to look at your trichomes through a magnifying glass. Clear= not ready. cloudy= reaching maximum thc levels. Amber= the thc is starting to convert to CBD and other less desirable chemicals. The plant will slow down growth and you will notice the little buds swelling up. The hairs will start to die off. It is a good idea to start monitoring your trichomes when you have about 50% brown pistils(hairs) she will be close then. Good luck