Cool How Long Should Toner Sit On Hair References. Web toners should be left on the hair for between 15 and 20 minutes, depending on the brand’s instructions, and up to 45 minutes if it is specified in the. Hair should already be blonde.

Depending on many factors, including those that you can’t control, the toner you’re left with from the salon should last about 6. In case of brassiness, you should keep the toner on. During regular services, toner application usually.