20 - 30 minutos
Putting a new battery on my 3GS
It took me over an hour to disassemble my iPhone to change the battery and reassemble it: it was my first time.
But... wait... my camera didn' t work!!!
I did it all again, more carefully this time - especially putting the camera module back in place - and at the end it all worked fine: and it only took me TEN MINUTES! :)
Be very careful but don' t be too scared: you' re doing what a professional does many times a day