10 - 30 minutes
So the big bad boss man - a rather intimidating, old, rich guy that rules the office with an iron fist even in areas he has no expertise (like server room cooling) - says "the battery in my iPhone keeps dying... replace it". I first try the usuals... reboot the phone (full power-down, not the iOS 5 "hibernate" shutdown), close apps, check settings... and give it back to him hoping it's fixed (but no way to check). He comes back again with the same 14%-depleted-at-10AM battery problem. My iPhone 4S is at 96%, his is at 86%. Something's wrong, but I know it's not the battery. I order it anyway.
Great. "This'll just take 5 minutes". Screw screw, slide off cover... the plastic opening tools were near useless in the process, though - do NOT recommend using them, they just bend the !&&* out of the malleable LiPo battery cell (and you do NOT want to do that). Got the pack out, put the new one in, screwed it down, slid the cover on, screwed it down, and turned it on. Gave it back to him and showed the battery now half-charged as an indication of the new battery. Haven't heard from him since. But out of curiosity, I put the old battery in my own iPhone 4S. The next morning? 96% charged as usual at the same time. Hmm...
As is often the case in the corporate world, just do what the boss says, even if you know it's wrong. At least your boss will shut up about it and you keep your job. :)