5 - 20 minutos
My Xbox had already had the RROD, I had sent it in once to someone who "knew" how to fix fit, then it got it again.
The repair was pretty straight forward, i had bought the kit, just followed the step by step tutorials on the RROD fix, re-applying thermal paste, and reflowing the board. It's been about a month now and it's still running RROD free.
Take your time.
Metal Spudger Set
Arctic Silver Thermal Paste
Xbox 360 Red Ring of Death Fix Kit