1 - 2 Stunden
My PS3 switched itself off 5 minutes into a gaming session, and would not turn back on after that. It would try to spin up, then blurt out 3 quick beeps and show a flashing red light that I could not stop without switching off the unit on the back.
After finding the right teardown guide on youtube it was a piece of cake. The guide on iFixit is for a newer model PS3. My machine had a different power supply and a much smaller motherboard. The basic tecniques were identical though, and cleaning out dust, heating up the processing elements, and reapplying thermal paste did the trick!
As you break down the system, separate your hardware for each step. I used small tupperware containers and iFixit has a nice looking magnetic board that looks like it would be great for the task