you can judge flowering time by color of pistil hair but that's not the best way to do it. The best way is to get a magnifying glass or hand held microscope ~30x and look at the trichomes. This are little golf tee looking things that start off clear and slowly turn white. After turning white they start turning amber. Depending on what kind of high you want determines when you should harvest. If you harvest earlier with no amber trichomes it will be a more head high, if you harvest later with some ambers you will have more of a couch lock high. These trichomes are the thc that get you high, once they start turning amber it means the plant has peaked it's thc potency. Hope this helps.