Blog post: swansont: A Song Should Be Just Long Enough to Reach the End

Why Are Songs on the Radio About the Same Length?

I think there are a lot of reasons, one being that radio stations are not services that play music for you — their business is to air advertisements and use music as one of the hooks to get you to tune in. So long songs would not tend to be selected if they would keep them from airing ads, and that may be enough in the evolution of rock-era songs to keep most of them short. I think Rhett's gone off on the wrong path by looking at this in terms of how much music you can get on a 45 rpm single.

There's probably a lot more to this. Writing longer and keeping it interesting without repetition has to be hard, especially if you've gotten into a habit of a certain style. I remember seeing an interview with members of The Who (I think it's in "The Kids Are Alright") where Peter Townshend says, in relating how Tommy was written, that "rock songs are 2:50 by tradition" and then got the idea of writing a longer theme as a series of short songs.

But this animated gif of the action of a needle on a record is worth the price of admission.
Read and comment on the full post