30 minutes - 2 hours
My 24'' iMac hard drive went crazy and began a phase of advanced autodestruction.
The guide is really precise and easy to follow. Some steps are a bit more technical, but the comments help with tips&tricks.
Don't hesitate to lever the front panel of the iMac (without pulling too hard on the camera wire), because the bottom of the panel (close to the RAM slot) has a "C" shape that holds the things together.
1 TB SSD Hybrid 3.5" Hard Drive
iPod Classic (Thin) Replacement Battery
Pro Tech Toolkit
iFixit Opening Tool