Macbook pro stuck on 'About a second remaining' for an hour
The problem with the upgrade script is the timing only estimates how long it takes for Apple's software to install.

You can (and should) open the log file while upgrading/installing and press Command-3 to show all logs, not just the errors.


⌘+L
⌘+3


You can see that during this "about a second" it's really migrating user files and handling all the things you've brought to the Mac that isn't part of the base system.

Basically, let it run as long as you can stand - especially if the log file shows progress being made. If progress isn’t being made, consider connecting to the internet via a wired connection if possible or making sure the wireless network is operational before interrupting what looks to be a paused or stopped installation.