I still think Re-Fried Boogie - Canned Heat, wins, clocking in at 40 some odd minutes.
For a song....I think I mentioned the 22 minute version of Tall Ships by Show of Hands, from their current two CD best of, though rumour has it that Fairport's Sloth gets longer and longer with each performance *LOL*

Charlotte (the view from Ma and Pa's piano stool)