Bathroom breaks and bit of eating allowed, the official record is 15½ hours - of a little shareware F1 management simulator where the free version didn't allow saving, so you'd just have to keep going as long as you wanted to make most of each game.
Next are Detroit (car manufacturing simulator) 14½ hours and Dune 2 with 12 hours.
There's couple non-turn-based games I've played over 3 hours without pause, in actual continuous gaming (aside loading screens or such).