I would say about 2 weeks and then check the trich's with a loop as mentioned. Most grow shops sell them nowadays. . .
Always go on the trich's. I cut many plants too early just because they looked ready to me, but when you take a look at the trich's they mostly clear some milky. You want about 50% amber, at least that's how I judge. More amber the more heavy the high. You don't want ALL amber though otherwise you end up with a batch of sleeping pills.
You will also notice with a ready plant that it loses that sheen to it, it starts to look more of a matte finish than sparkly. That's the trichs going from sparkly to cloudy / amber. Also take note of the leaves, they will start to change color, normally like a purplish color. Although not all strains will do this.
The way I can see immediately that yours aren't ready is the long white pistils. At least 70% should turn brown and shrink into the bud. White standing up like that is definite sign that she is not ready.
Hope that helps