long hairs = more time.
once you get the full plump and can't see it plumping any more, start scoping trichomes on the calyxes -- at different levels on the plant so you get a good perceptions of development. The percentage of amber is your trigger. The exact point you harvest is personal preference that others cannot figure out for you. you can harvest some buds early middle an dlate and test to shorten that learning curve. If you like sleepy buds, go for more amber on the bulk of it, but still cut off and label a few buds at different ripeness so you can test it out in 1 grow as opposed to several.
There's some variance to this, but once calyxes are fully plump, i find it still takes another 7-10 days to see the trichomes mature. I prefer an earlier harvest window, for reference.
Some rare varieties will barely show any amber even if you wait so long that the buds die on the stem. Not something you can predict, unfortunately. If something has been fully plump for a long time an dthe pistils are all dead and coild up, sometimes you harvest without the targeted percentage of amber trichomes. So, while trichomes are the best option to determing when to harvest, use other physical characteristics to help make the decision, too. Bud density and pistil coloration are not as good of indicators, but sometimes it's all you got.