2 - 4 heures
My sons dropped out iPad several times and it survived amazingly well until the last straw and then the display cracked.
The repair went fine--about 90 minutes. Only confusing thing are those many small foam spacers which are semi-attached and I'm not sure which, if any, I'm supposed to keep. The instructions were silent about these little items. It appears the new unit comes with spacers, so I cleaned them out, but the instructions should probably make explicit mention of them.
Also, the instructions tell you to start prying in the upper right corner which is where the power button is and it seems like it's possible to mess up the power button with the metal spudger when digging around up there for the first time.
This repair looks daunting, but don't be afraid. I would recommend a pair of angled tweezers to help guide the connectors back into the sockets when reassembling. They're a bit hard to reach with just fingers because you can't just open it all the way up--you have to hold it half-way closed for the connectors to reach the sockets.
As with all such things, read the instructions all the way to the end before starting!