1 - 3 heures
Dropped my gs4 on a tile floor, the Liquid crystal started leaking into the glass area and it stopped responding to touch. It was pretty useless after that.
With the tools and guide, the repair took around half an hour in total. I kept the screws and parts grouped together on the desk, so it was pretty easy to reassemble the phone after pulling off all the components.
For a digitizer repair, it helps to watch a walk through beforehand, it helps to hear how removing and assembling the parts sounds. And definitely assume that each component might have a little extra adhesive or something that might make removing the components tricky. Took it slow on the front facing camera and other parts along the top. Other then that little detail it was a snap.
Phillips #00 Screwdriver
iFixit Opening Tool
Galaxy S4 (AT&T/T-Mobile) Screen Assembly