Either in terms of overall play time or just in one session.
The first time I played Oblivion, I was not aware I could lose track of 32 hours.
I've lived over an actual month in Skyrim, that includes eating, sleeping, and wanking
(That's .4% of my life)
[spoiler]#Gaming[/spoiler]
-
Went through the entire halo CE campaign on legendary when it came out, 14 hours