Some older machines suffer from a system clock that systematically loses time, resulting in your operating system, in this case Ubuntu, displaying the incorrect time and in the process causing you to be late for all you carefully scheduled appointments, unless of course you have a second time source on hand.
One way to avoid this is to force Ubuntu to keep its clock synchronized with Internet servers, meaning a quick check on boot up, and a time that should always be pretty accurate, unless of course you don’t have network connection and your system clock failed miserable at the last power down sequence.
To install NTP, simply open up a terminal window and execute:
sudo apt-get install ntp
Reboot your machine and voila, your clock should now be reflecting an accurate time for your selected time zone! :)