If you want to be played on the radio you need to create a 3 minute song.
You need a good 3 minute song for a movie soundtrack.
If you have something say to say or you want to create a musical work; you make go as long as it needs to. Maybe 5 minutes? Maybe like Yes did…you make a song that covers an entire side of one album.
Arcade Fire – Sprawl II (Mountains Beyond Mountains).
A bit longer than 3 minutes but worth every extra second.