How long does henna need to stay in your hair???

So I finally purchashed some Henna....and I am ready to use it. I was just wondering how long does it need to stay in your hair to get the strengthening affects that it gives. The added color affect is nice but that doesnt matter that much to me right now. I know many of you ladies sleep with it, but I am not sure I will have the time to wash it out in the morning and do a deep and all that fun stuff so can you all ladies give some tips...thanks

I read that 4 to 6 hours is good. The shortest I've ever kept my henna in is 6 hours.

Thanks for this info guys! I'm doing my first henna tonight!

I agree 4-6 hours should be sufficient for strengthening and color release. Please let us know how your hair turned out.