density has alot to do with how powerful of a light your using. if you dont mind me asking, what do you use?
8-9 weeks is avg, but you really harvest based on the trichs, not what the avg is, you want mostly milky, when you see amber trichs the thc is degrading, clear and it hasnt developed fully
if u want, harvest the plant in 3 parts, some when its 50/50 clear milky, some all milky, and some with some amber trichs.
should only be a couple days apart each
you will get a different high depending on when you harvest, test it out and see what you like best