Invest in one of them Jewelers eye socket things, you can get one for as low as £19, Has x30 magnification and a smal LED. What you are looking for is the little trichromes, they look like small hairs with a bubble at the end of them, kinda like mushrooms and their caps. Initially those will be crystal clear, to the point of shining, that means its too early, then they become milky, still crystal clear, but dont shine as much anymore, and then, they become amber. When you harvest your plant when the trichromes are more milky than amber then the high will be heavy on the head, usually thats a good practice with sativas, whereas when you harvest them when they are 10% amber, then the high becomes heavy on the body. If you leave them longer than that the THC will convert to CBN.
A good suggestion would be to begin your "flush" when those little trichromes become 90% milky, by the time the flush ends youll have about 5-10% amber trichromes which is the perfect time to harvest. Be patient and look everywhere, bottom buds, top buds, you can even pluck one of the smaller buds, open it up and look at it with that loupe.
Your plants look amazing, and the end result will be rewarding, be patient and observe well :D
I hope this helped, Best of luck <3