When I first started writing lyrics/melody I never gave it a thought about the length the song would be when finished. So many, early on, were just too long, too many words. No room for the musicians. Over time I learned that my writings and songs improved when trying to be more consise with my words and leaving space for performance and arrangement.
I'm not always successful, but ideally, I try to keep a song I'd like to demo or market, under 4 minutes, (as close as possible to 3:38).
With that said the song can also become an extended version with it's own appeal and purpose.
I have written 1 "song" that's around a minute, and my good music bud let me know it's not a song because of it's missing parts. So I call it a diddy
@MikeRobinson, your mentioning "repeating" reminded me of King Crimson's Indiscipline. I had to cue and crank it up. I added a link in the music lounge topic "what are you listening to"