Best (and only accurate) way to tell is by trichome colour under a scope. Clear is underdeveloped... Milky white is fully developed... Amber is starting to degrade.. Milky white trichomes will generally produce a more up-lifting/energetic high.. where as amber will give you more of a lazy/couch stone. I usually recommend to harvest at about 30% amber.. but it is really all in your own personal taste! Sounds like you could flush for 7-10 days and wind up right around the 30-40% amber mark at this point.. if you leave them a bit longer you will get a more "couchy" high.. Hope this helps!