I don't really know.
I know the longest session that got logged anywhere was Zelda Twilight Princess on Wii at exactly 11 hours about 3 or 4 years ago. Was my third play through (4th if you count GC version playthrough) and I wanted to hurry up and get to the Arbiter's Grounds already. I don't think I ever finished that playthrough though, should be at the Temple of Time or the City in the Sky.
Otherwise I'm pretty sure that isn't my longest time playing a single game. I'm positive I topped that a couple times with a session of SimCity 4, Rollercoaster Tycoon or any of the Total War games. There's no way to know though, sadly.