As far as I can tell, this is the record (albeit unverified) for recorded solo piano performance length. To prepare, I didn’t eat or drink for a 24 hour period. By the 33rd hour I was hallucinating; I ended the performance after realizing I had passed out.
Vexations gives a speed of très lent with the caption
Pour se jouer 840 fois de suite ce motif, il sera bon de se préparer au préalable, et dans le plus grand silence, par des immobilités sérieuses
(In order to play the theme 840 times in succession, it would be advisable to prepare oneself beforehand, and in the deepest silence, by serious immobilities)
with two variations and a theme to be repeated. (lilypond source for score can be found here.)