20 - 30 minutes
Over the life of my iphone the battery has lasted less and less, it has finally go to the point where I have to charge it twice in any given 24 hour period just to keep it useful.
The repair went very smoothly, with one minor hick-up. When putting the phone back together it was kind of tricky to to get the ribbon cable into the connector, which is disconnected as step 6 in the guide. Other than that everything was pretty easy and will documented in the guides.
A pair of tweezers or forceps may have solved my problem during re-assembly.