40 minutes - 2 hours
Ear speaker on iPhone 4 went out. I could use speakerphone (the bottom speaker) but not the one at the top of the unit. It was annoying, inconvenient. Audio quality was bad.
The friend who recommended iFixIt volunteered to do the labor if I bought the part and the required tool. He followed the instructions. It all worked fine. He removed many tiny parts from the phone, so I was a little concerned, but it all went back together and it is working now.
Follow the instructions, be patient and don't lose an parts.