It is important to prepare your skin for a spray tan. It is just as important to take care of your tan after it is done, to make it last as long as possible. You can rinse it as early as 8 hours, after 12 hours it stops processing, no merit to leaving it on beyond that time and can increase the potential for ruining it. Best to get it off and never leave it on for a full 24 hours.
Read some more tips that will help increase the life of your new tan @ http://www.internetbillboards.net/2015/10/28/make-your-mobile-spray-tan-last-longer/.