i usually harvest after the dark period...but try it at different times. i honestly don't think it matters as long as the flowers are ripe. i use the trichomes as a timetable for harvest...appx 10% turn amber-red, it's time. other's use the hairs...but i've found hairs will turn faster under strong light/sun and intense heat and is not a sign of maturity. (i'm in the desert sw and it's hot n sunny all summer...your environment may be different)