10 - 40 minutes
The phone decided it didn't want to fit in my pocket any more, and made a leap for freedom. It landed in the one way that its case couldn't protect it from. The bottom half of the display practically turned to glass dust and destroyed the digitizer as it went.
Surgery was performed over the course of an hour. Patient was resuscitated without incident.
Anything thin enough to slide under the back case to release the glue is thin enough to cut you - mind your fingers and be careful of the pressure you're applying.
The amount of force needed to separate the battery mount from the motherboard will surprise you. On a related note - take note of the clips when you're reassembling it.
Take your time. Double check your work. Don't rush, and it will work fine.