I bought powder henna at a health food shop. It is currently on my head. I used to dye my hair with henna all the time, but it was Lush's henna which I've heard is not "real" henna. When I was using Lush's henna (which, from what I understand, is significantly watered-down) I'd leave it in overnight. But the package for this brand said 45 minutes-hour. Any henna users want to weigh in?