This will differ on a case by case basis. There is no set timing. We recommend checking your lightener frequently (every 3-5 minutes) when working with higher volumes, compromised hair or while using heat. Please note that although lighteners are the same in regards to chemistry, the strengths may differ. As some lighteners provide 9+ levels of lift and others only 5, the amount of Olaplex may be adjusted based on the specific product you are using to achieve desired results.