1 - 2 Stunden
My nephew gave me his PS3 because it had a YLOD and rather than fix it himself he bought a new one and gave me his broken one. He said if I could fix it I could have it.
I must admit I was slightly intimidated by the repair. I didn't want to make a mistake. Overall it took me about 4 hours. I took my time and made sure each step was done correctly. I would say it was not hard but not easy. After this experience I would have no problem doing a YLOD repair again.
Pay special attention to reinstalling the blue-ray player, on/off sensor and the power supply. Power supply make certain you have the ribbon and the plug secured properly. The blue-ray player ribbon is tricky to set correctly, use kid gloves. The on/off sensor be careful when putting the top cover back on, it is easy to knock the ribbon out if you did not put it in fully. I wound up having to take the cover back on and off about 3 extra times because of these simple mistakes. One other piece of advice, enlarge the pictures from the guide... very helpful. Also label your screws and parts according to the steps, it makes reassembly much easier