I do it myself, so I don't really time it. Usually stick the bleach on to lighten it a bit. That stays on for 20-30min gets washed off then I stick the colour on. Once the colour is on I'll wrap it in tinfoil then go watch a movie, read a book or play some computer games. Eventually I'll rinse it off
The blending is much easier than I first thought, yet turns out really cool.