How Long to Leave Hair Dye In (Permanent, Semi, and Toner)Over-processing is the number one hair dye mistake. Here's how long each dye type needs — permanent, semi-permanent, bleach, and toner — and what over-timing does to your hair.Frequently asked questionsIs TimerRush free?Completely free — no account required.Where can I try the timers mentioned in this guide?All timers are at timerrush.com. Bookmark /t/25m or /t/5m for quick one-click access.