5 - 15 minutes
I wanted to replace a hard drive to keep a late 2008 MacBook going. While at it, I increased ram from 2 to 4 GB.
Extremely well. The most difficult part was setting up a Yosemite bootable thumb drive. Hardware removal/installation was simple because the IFixit guides were so clear. Repair took about 6 hours because of the need for a bootable source.
Start by making sure that you have a reliable source for booting once your repairs are made.