1 - 2 horas
Turned on my PS3 one hot sunny day and got the dreaded YLOD.
It took a few hours because I was trying to really careful with the screws, clean parts along the way, and also because I took a couple hour break during the motherboard cooldown step.. just to be totally sure it was cooled enough. So, total time about 4-5 hrs. UPDATE: My PS3 worked for about a week, and then it died again. Make sure you back up your data right after you get it working again! I forgot to do so and now I have to repair it again to salvage all my saves. Sony apparently makes it difficult to get saves off of your HD and copy them to another system if your PS3 dies.
Just follow the guide along with the video ... they are done pretty well. There were a couple steps I did out of order.. for example when I pulled the top cover off, the memory card reader came up with it, so it was a tad confusing when I looked at the guide and couldn't find it at first. Also, on some of the steps I took out more screws than necessary, so had to refer to photos to find out where to put some of them during the re-assembling phase. Taking pics along the way is a good idea!