Why do EDM musicians often create an intro that is 15/30/45/60/120 seconds long?

Question

Not all tracks have intros, and usually those are extended mixes that have them (sometimes can be original mixes and remixes). However, I notice that often their intros are 15/30/45/60/120 seconds long, or taken in minutes these numbers are 1/4, 1/2, 3/4, 1, 2 minutes. So, is there some kind of rule? Or is simply their inner OCD and these numbers are some kind of key numbers in music? A few examples (links to beatport): [D.O.D - Glow (Extended Mix)](https://www.beatport.com/track/glow-extended-mix/10626415) [Lush & Simon - Callin' (Extended Mix)](https://www.beatport.com/track/callin-extended-mix/10638813) [Apster - Photobomb (Original Mix)](https://www.beatport.com/track/photobomb-original-mix/5066274) [Swanky Tunes - Fire In Our Hearts feat. C. Todd Nielsen (Arston Remix)](https://www.beatport.com/track/fire-in-our-hearts-feat-c-todd-nielsen-arston-remix/6370003) For tracks that I looked their BPM was in 124-128 range, but I guess the actual range is wider than that. As you can note they are of slightly different genres and these were only 4 examples.

Answer 1

For club-based tracks like these, a song will often-times have a long, non-musically-dense intro (as in, it'll often only have the drums & one or two simple elements. Generally, the song gets a lot more dense & complex later on). This is to make it easier to transition to the song in a DJ set; the long intro affords the DJ to introduce the new song via 'baby steps', if he choses. If not, he can skip right to the 'meat' of the song, but it's nice to have the option of both for more flexibility.

Overall, when writing the intro, the exact time down to the number of seconds isn't really thought about. What's more important is the amount of measures of music that are used: 4, 8, 16. 32 etc. Of course, the addition of more measures is always going to equal out to the addition of more time too.

Sometimes, when writing the intro, a person may initially 'feel' that their intro should be so-and-so long, in terms of a loose length of time ("pretty long", "immediate" etc. moreso as gestures than as exact times), but it always needs to be exactly quantified in the amount of measures (when it comes to most dance music, at least) in the end.

I hope this helps!

Answer 2

There is no rule. In most cases these are responses to how the public reacts to it. Everyone studies everyone. You should too. If they are having more sales or plays creating intros with those times, then you should to as to compete with top composers and creators. Also to change with the times. if your music doesn't have what the "new sound" has then yours can seem dated. I hope this helps.