There is no exactly right time to harvest. It is a matter of grower preference, with some ground rules. I've never been able to grow anything other then males, so I'm not talking from experience here.

But, from what I've read, basically, when the trichomes start going from being clear inside to cloudy inside, you can start to harvest. Or you can wait for many of them to turn amber colored inside.

The more amber trichomes give more of a "couch lock" type of "stoned" high, the cloudy trichomes give more of a "cerebral" or "energetic" type high. The main thing is not to get it when they are all clear, and not to get it when they are all amber. Clear trichomes do not have the drug your looking for developed in them yet. And amber trichomes are dying and losing potency... so if you pick when they are all amber, many will die as the bud matures while it cures.

If I ever grow a female, I'm going to harvest some of her buds at cloudy, some at amber, and some mixed in between... that way I can compare and contrast and see what I like. You might want to try something similar.