5 - 30 minutes
The 15"MacBookPro which I sold to a friend last year and he brought it back in March saying it sometimes wouldn't boot and was making grinding noises. OH NO! Thankfully there was nothing important on it. I couldn't even get to reinstall OS X.
After ordering a new HDD, I replaced the old one. A simple and straightforward task. I had added memory the year before. Reinstalled OS X. Hey now it even has Yosemite!!
Along with installing some other programs, I say it took about 2 hrs.That included installing Yosemite twice as I was installing from a flash drive and it rebooted before I could stop it.
As long as you have the right tools and parts, GO FOR IT!!