1 - 2 hours
The power supply died on my iMac. I mentioned to my son that if he helped to fix it, I would give him the computer. (I had already purchased its replacement for my business.) He quickly agreed after looking at the instructions on iFixit.com.
It took the two of us less than half an hour to make the repair. We were both shocked at how easy and quickly the repair went. Both of thought that we had to have missed a vital step. But, the computer is running just like new again.
Our only advise is to read the instructions before you begin. Then read the instructions again. We made ourselves very familiar with inside of our computer before opening it up by looking at the photos and reading the instructions.