forever and a day. when it looks like actual weed, then you can start counting days. get a 30x or greater magnificaion - can just be a cheap currency checker, for example.
google - trichomes. 10-100% amber depending on who you ask and everyone is right, if they have tried it all and settled on someting they like. try early middle and late amber development and see what you like. ignore any preordained amount of time as it is at best a guess and definitely irrelevant to reality of the plant at hand.
the more you think about it, the longer it takes. the more you do it, the less anxious you'll be about it. 'amber' is degredation of active ingredients. don't think it's the 'strong stuff'. there's a whole portion of the plant you cannot see. at this point in the game this is more art and anecdotal nonsense than science. even with better knowledge, you still want to try different points in harvest window. not all drugs affect people in the same way. nyquil may make most sleepy, but some percentage gets hyper. your brain chemistry might be a little different, who knows?