is good time to harvest ?

That entirely depends on what you want from your smoke... early harvest will give you a more cerebral high... waiting until the pistils are about 50% brown and the trichs are more milky than clear will give you a rounded cerebral-and-body high... late harvest, when the majority of the pistils have turned color and the trichs are more amber than not will give you couch lock - but beware that the later you delay harvest, the weaker the THC will be. It's all in what YOU want... Good luck!