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.

I was worried about the same, until it finally went through. I opened the log and it was getting a lot of errors, but while I was reading about this on another computer, it suddenly finished with a message that everything was copied and it automatically rebooted. I was performing a clean install of El Capitan on a new Samsung 850 EVO SSD on my MacBook Pro 13" mid 2012. I guess the key here is just to be patient.

I had the same one second remaining and the log said it was trying to verify the installer. I plugged in my ethernet cable and couple minutes later it finished.

I had this problem and realized it was because I was not connected to the internet. Connect to either WIFI or plug in an ethernet cable and the install will finish in a few mins.