When checking trichomes look in the centre of your flower - not the top. The tops ripen faster - get a good average from the centre / middle of the flower.
As for when, trichomes have to be atleast milky in the middle of the flower - clear = no THC, milky = THC peak, Amber = THC degrading.
The thing is the flowers dont all ripen the same time - look over all/most of your flowers to get an average of where she is at.
I harvest when i have about 10% - 30% Amber. The more Amber the more couch lock / body stone you'll get.
Good luck, hope this helps.