You need a closer look at the trichomes, a jewelers loupe should be able to help you get a closer look. I typically like to harvest at about 50% amber heads. When you use the jewelers loupe you will be able to see how close you are way more clearly. But by the looks of this picture since it still has long white hairs I’d say Atleast 2-3 weeks. Depending on strain and the average time it takes to harvest that strain you could also go off that way if a jewelers loupe is out of the question.