2 - 5 minutes
My wife had a cover on her iPhone, so we didn't notice that the back glass had shattered until we needed to replace the cover. I knew the tools and materials were available, and after looking around a bit I went with ifixit.com because my past experience with you guys had been so good.
Super easy. I also liberated her iPhone (replaced the pentalobe screws with philips ones) to make future repairs easier. I love that you guys include that too.
If you're the type of person who is not afraid to try fixing your own stuff, ifixit has the goods to get you over the edge. Just order your kit, follow the instructions, and be the hero.