2 - 5 minutes
Dropped phone caused front screen not to function--it still had touchscreen ability, but you could not see anything!
Took longer than the one hour that was indicated, probably 2x that. In the end, everything is working like new!
The repair toolkit was worth getting. Stay organized by either taping the screws to a printout of the directions, or use cups of some sort to separate the screws and pieces from each step.
iPhone 4S LCD Screen and Digitizer
iPhone 4 Earpiece Speaker
iPhone 4 Home Button Assembly
iPhone 4 GSM OEM Used Rear Glass Panel