Songs of right length

You usually don't have to worry about your tunes being too short, but in the rare instance of having a favorite tune that's only one minute long, you can make a double or triple-length version easily, splicing together repeats of that tune, into one longer version, while maintaining the beat.  Music editing software is a good way to do this.

The far greater problem is a tune lasting too long, usually meaning more than three minutes.  It's a twofold problem.  (1) Most social dancers would prefer to have four 3-minute dances with four partners than two 6-minute dances.  Variety and contrast are good.  (2) Many leads/men feel that their repertoire of freestyle dance figures is exhausted after two or three minutes, and they would much rather move on to something else.

Since many recordings are longer than three minutes, you have two choices: fade the song out at about three minutes, or edit out a central part to retain the original ending.  I always listen to the original ending to see if it fades out, as much popular music does.  If so, then I'll know that an earlier fade-out at 3 minutes is okay.  But if there's a definitive ending (which is especially important in swing and tango) then I'll edit out some central strains to bring the song down to three minutes.  If the song is four minutes long, I'll listen through the piece several times, searching for the minute which I can remove from the center without harm to the song, usually a verse and chorus among many repeats of that verse-chorus.  If the lyrics are telling a story, you might worry about removing an important middle part of the story.  Don't worry — dancers are too occupied with dancing to be listening to the lyrics.  Once again, there are plenty of software options for editing middle sections out of music to make a 3-minute dance version.

Exception 1:  Some fast and exhausting dances might want to be shorter than three minutes, like a fast techno polka for instance.

Exception 2:  Some dance traditions favor long songs, like salsa.  And some groups are so specialized, like West Coast Swing clubs, that the leads know hundreds of variations for that one dance form, and are happy with longer songs.  Good DJs ask what the dancers prefer, including song lengths.  Dancers' wishes always come first.