The first single to get number one on a pop chart that was over 5 minutes was Dylan's "Like a Rolling Stone" at 6:11 (Don't you think it is sad I can qoute the time off the top of my head? I do). Dylan has done a lot of good songs over 5 minutes that tell amazing stories. The great thing about his tunes is the way in which they don't develop, as odd as that sounds. An amazing feeling is built up by the unending verse-chorus repeat, that gets you into a kind of trance, like "Sad Eyed Lady of the Lowlands", or "Idiot Wind".
Of course, this kind of thing happens in jazz all the time. There is a great Australian Jazz band called The Necks, who are a Piano, Bass, Drums trio, who tend to only perform one piece at each gig they do. I have a couple of their albums, that have pieces that go for up to 63:29 and the shortes is 53.24. The way the pieces progress is amazing, sometimes they change a lot, and in the longes one called "Black, the pianist and bassist each play their own motiff that repeats for the whole tune, it is the kind of music you shouldn't listen to at midnight (or rather, you really should, just don't expect to come through the night sane). I know this is off the topic a bit, but hey, it struck me while I was thinking of great long songs.