Friend of OPC Joe sends over the following link in which a blogger named Joshua Allen for something called The Morning News asserts that the perfect length for a pop song is two minutes and forty-two seconds, coughing up such 2:42'ers as the La's "There She Goes," "California Dreamin'," "Lovely Rita," "Divine Hammer," and Guided by Voices' "Echos Myron," which is so good it makes me salivate, but lets not get carried away and think it was any kind of hit.
It turns out that in 2004, another person had posted a comment on a blog positing the same principle with the exact same song timing, also citing "There She Goes" and adding such hits as "Johnny B. Goode," Patsy Cline's "Crazy," and two songs by Tom Petty and the Heartbreakers, which is at least one too many.
These guys appear to have approached their respective projects as I would have - they sorted their iTunes by song length, then looked for the time that had the best songs. Thus you get them seeing the Beatles' "Michelle," saying "Yeah, that's a good one," and chalking it up to the magic of 2:42. But "Michelle," as delightful as it is, can't be one of the Beatles' twenty best songs. If you want the perfect song length, you can't just say, "Eh, that one's OK." You've got to have perfect songs. (I will note that my iTunes spits out, at the magic 2:42 mark, "Will You Love Me Tomorrow" and "A Lover's Concerto," both of which are nigh-on perfect.)
The right way to do this would be to compile your list of the best thousand or 1500 or whatever songs, then note which time comes up most often. Or you could look at the lengths of perfect songs, and see if any others match up. Let's see...
"I Think We're Alone Now": 2:12. Others at 2:12: "Janie Jones," "When Will I Be Loved" (by Linda Ronstadt)
"Both Sides Now": 3:16. Others at 3:16: "Beverly Hills," "Kentucky Rain," "Summer Babe," "Alex Chilton"
"Hey Ya!!": 3:59. Others at 3:59: "Tempted," "Photograph" (by Ringo), "The Boy in the Bubble," "19th Nervous Breakdown"
Hmmm. Based on this rudimentary research, I'm going to assume that 3:16 is the perfect song length. I'm surprised at how well 2:42 held up, especially with "A Lover's Concerto" thrown in there, but I sure love me some "Beverly Hills."