Put on your processing cap and let the hair sit for no more than 20 minutes, though Dorsey stresses that it can take even less. “You want to keep a very close watch on the hair, depending on if you want the hair to go to a warm blonde or a cool blonde,” explains Dorsey. Platinum blonde hair dyes have a rep for taking an eternity to work, but I was ready the plunge in getting bleach blonde hair, to which the answer is: not really. If your hair is already bleached or naturally blond, then it might be worth a shot to try a home kit. Is bleaching the right technique for me? Much. Whether you're a natural blonde looking to go blonder, or a brunette wanting to cross over to the brighter side, you're going to be lightening.