Majin-Tenshinhan on 07 July 2009
I've probably had longer ones than this, but a few years back I sat down and started a new file on Super Mario 64 and gathered all 120 stars from memory (Refused to use FAQs etc. when I forgot where a star was). Took 13½ hours.
EDIT: Oh wait, there was that one time in FFX when I was farming everyone's ultimate weapons and I ended up with a, like, 20 hour session. Played through the entire night and went to bed at like 9-10AM the next morning.
