3 hours
The optimal timing for a root touch-up is when there is 4 to 5 weeks of regrowth, approximately 1/2" to 1". Longer roots make achieving a uniform root lift more challenging. Hair beyond the half to one-inch regrowth may not lift evenly due to the reduced heat from the scalp, resulting in banding. In such cases, a different technique will be necessary, requiring more time for the process.