If you're using Madison Reed's at-home root touch-up kit, you'll want to leave the color on for about 30 minutes. This will give the color enough time to develop and penetrate into your hair shaft. If you have very porous hair, you may need to leave the color on for a bit longer. Just keep an eye on your hair and make sure the color isn't getting too dark. You can always rinse it out early if you need to.