Very straightforward battery replacement. Your photos are the key.
20 - 30 minutos
Old battery in my wife's iPhone 3GS would not hold a charge.
The take apart went very smoothly and quickly. The only minor glitch was getting the battery positioned perfectly so that the board would fit the screw holes. It only took 2 tries but I would make certain that the battery connector area was flush - the first time -next go-around. In all, very smooth
Not really; once again, your photos and explanations of potential trouble spots are spot on and extremely well done.