it's ready to cut when you can't wait anymore.. :P

no it's really up to you... harvesting at different times will produce different types of high.. hopefully you've stopped giving it fertilizer.. you should water with just water for at least 2 weeks prior to harvest, this gets out the excess salts and nutrients.

if you're unsure, try cutting some now.. some a week from now.. and the rest 2 weeks from now.