I've been dying my hair auburn for three years now. Despite this I have tried maybe only three brands of hair - that is Lush, Superdrug and Henné Color. Recently, natural henna hair dye brand Khadi* got in contact with me asking me if I wanted to try one of their colours. Jumping at the chance to try a new brand (I still haven't found a brand I love) I was immediately smitten with this brand.
As with all henna, the minimum time the dye needs to be on is half an hour, and can be left on until two hours later depending on how bright you want the colour to be. I personally left mine on for an hour and a half, which resulted in a very natural auburn shade. As you can see from the photos, my hair doesn't look that different - this dye just simply helped me re-do my roots and create a natural looking auburn shade. The before picture has a bit more ginger in it due to the Superdrug hair dye from last year still being present (it's what gives my hair a slight ombre look) and the dye helped darken that out. My hair is naturally medium brown so if you're blonde it might come out darker. The final colour was very similar to the colour I get when I use the Lush Henna Dye (the Henné Color was the brightest).