I think rather than constantly showing the correct time, it has something to do with whenever the page you're viewing was last updated as well as with the users visits.
For instance, when I have been offline for a day, and I visit a forum, it will show the correct time when I visit the first time, then keep showing that time until a new post is made in said forum or until my cache is cleared or something.
[This message has been edited by Defibrilator (edited 09-06-2015 @ 11:22 AM).]