20 - 30 minutos
My iPhone 3GS' battery wouldn't hold a charge for more than 15 mins even at 100%. Quick googling of solutions referred me to the iFixit site, which turned out to be a great resource. Few days later, new battery in hand.
Very smooth repair. The whole process took no more than 15-20 mins, now my 3GS' battery holds as well as when i got it out of the box.
Great resource for the not-so-tech savvy individual. Good for average joe, Bad for repair shops.