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]
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74 hours, after I got off my Xbox I fell asleep for 24 hours.