As soon as I see amber, if ever, I chop. I've tried waiting for amber but it always takes weeks after I figure it's done before amber shows at all. Even now some of my plants are past de and no amber. You'd figure that a 1000W HPS would get them going amber quicker but nope.
If you do start seeing many amber trichs then it's up to you to decide how much THC you want to give up to amber so it can become CBN. I chop when almost all the hairs have gone red and at least 50% of the trichs are cloudy. Trichs continue to age and degrade after the plants are harvested too.
Also make sure that the trichs all have balls on top. I've been ready to crop a plant and when I looked real close half the trichs had no balls and it took another two weeks for most of the rest to fill out.
With all that pot you're going to grow you'll need help cropping. Want to buy a trimmer for half price?