5 - 15 minutes
I've had this computer for 6+ years. Machine has run strong and was modern enough to handle my family's current needs. The HDD simply filled up causing it to slow down and throw "startup volume disk is low" errors. 2 teenage boys and iTunes...
Even though I live in Tokyo, iFixit got me parts in lighting fast time - and at a reasonable shipping rate!. I'm absolutely satisfied with the service I received. It was easy to find the exact matching parts via the ID my mac feature on the site.
Never, ever, try to open a white 20" iMac! This machine was designed from the get-go, by Apple, to not be opened. Using the iFixit guide provided a lot of valuable information. I also found a few YouTube videos of people that made it seem so easy. In reality, opening this case was a major pain. Followed then by all the EMI foil. Knowing what I know now I would have wiped the HDD, resold it and bought a new machine ;-(