2 shattered screens and 2 underperforming batteries..
The first screen took a LONG time.. Mostly because it was my first time in the guts of the iPhone..
Second time went much quicker, and easier..
When you are at the step removing screws from the corners of the frame of the iPhone - just before you remove the display, go ahead and remove the headphone jack. Removing the jack makes replacing the corner screw next to it ever so much easier..
I also followed another users advice and used a separate small plastic container for each step of the process where something was removed, I then labelled the container so it was easy to go in reverse order to put back together.. The second screen, I already had labelled containers.
Lastly, get a good magnifying device , preferably mounted on arms,so you can more easily see all the tiny components you are dealing with.