Umm. I know this might not help much. But on OS X you can look in /private/var/log/install.log

It might be similar in Ubuntu.

Mine starts as:
Aug 31 13:15:37 localhost LCA[79]: Launching the Installer using language code “English”
Aug 31 13:15:37 localhost OSInstaller[166]: Mac OS X Installer application started
Aug 31 13:15:37 localhost OSInstaller[166]: 2 display(s) found.

That is the date I did a clean install.

Thank you. I was unable to locate an install.log on Ubuntu.

You can check /var/log/installer/syslog in Ubuntu, I suppose. It contains a log from the installation. At the beginning the time wasn’t synced though, so it’ll say it’s January 1st, but after a while (search for “ntpdate”) it synchronized your computer’s date with a server on the internet and will show the correct date.

You cannot view this file as a normal user though, so you might need to run the following in a terminal window:

gksudo gedit ./syslog

(Be sure not to edit anything!)

@Vincentt: Thanks!

For time:
sudo cat /var/log/installer/syslog | grep -n ntpdate

For year:
sudo cat /var/log/installer/syslog | grep -n “Hw clock” | tail -1