I sat through the 1992 revival of Einstein on the Beach, which goes for five hours, and which is much more static (as hardcore minimalist music) than a symphony would be. I had no problem sitting through the entire thing—even though the opera creators imagined you could walk in and out as you pleased. And I was proud to give them a standing ovation at the end of it.
(The audience was much more restless in the 1992 revival than the 1984 revival, apparently. There was booing in the bed scene. The people booing did not stick around for the standing ovation.)
The six hour TV version of The Mahabharata (1989 film)? Not a problem.
As long as the symphony is any good, I’m up for it. Just gimme a La-Z-Boy and a coffee, and I’m good to go.