I use my Amla oil three times a week, as thats what it says to do on the box. I have Dabur Amla oil, and it says:
"How to use: For best results, apply 1 to 2 teaspoons (up to 10 mL) of Dabur Amla Hair Oil into the hair and leave for sometime (ideally 1 hour). Then apply a good shampoo such as Dabur Vatika Henna Conditioning Shampoo. Massage the shampoo well into the hair and scalp. Rinse thoroughly. For best results apply Dabur Amla Hair Oil three times a week."
Then it notes that prolonged use can darken lighter hair. It has a little with me, I have brown hair...and its just become a deeper brown. Not black though, if you pay attention, you can see it still brown, Lol. It has helped my hair a lot in the month or so that I've been using. I'm pretty sure I use more than they say though, since I pour it into a spray bottle and spray it on all over my head.