When you talk about electronic music with 20 minute "songs" you're talking about various dance genres eg: progressive trance, psytrance, other rave oriented music. I have never heard anyone in that scene use the term "song". Tunes, beats, but never song. As for prog, I'm not sure you could call Jethro Tull's "thick as a brick" a song as such. My point is that once you cross the 10 minutes mark, it's unlikely that the person playing it will refer to it as a song.