The Grateful Dead played for five hours straight at Watkins Glen NY in 73. I was there. I stayed awake through it all, but as soon as the next band, the Allman Brothers, started playing, I fell asleep. I blame the Dead not the Brothers. Well, also that I'd been up all night walking in to the festival site.
Wouldn't mind 4 min 33 sec of a John Cage composition, but 639 years would be a little much.