There are a few out there that recommend different times, some as low as six hours, I vaguely recall one that stated 5 hours as well. I would personally follow whatever the manufacturer/supplier recommends. It has been formulated to work in a particular way so you need to follow the instructions. If it says 12 hours and she washes it of at 8 hours the tan has not had it's full developing time and also wont last as long or as well as it is supposed to. I have used sunless solutions before and their training and sales people are very helpful so why not give them a ring and see what they say.