How Many Times Do You Have To Listen To Understand A Piece Of Music?

I guess it depend on how one defines "understand"; there are always additional layers of understanding and countless ways our aging and the passing of the decades changes things.  For example, we "understand" Elvis's music and impact differently now that what anyone 10 or 60 years ago would have understood.

But if what we mean by "understand" is to appreciate, then its subjective in 101 ways.  Some songs we immediately fall in love with in a powerful way like a newfound crush ("Big Dreams" by Amyl and the Sniffers is my latest) while others are a slow burn into something deep and enduring (I listened to the Jimi Hendrix Kiss the Sky compilation many times over before I finally connected with "Third Stone from the Sun," a song that I don't know if I "understand" all these years later, but I do indeed love it in a very deep way, probably in part because it remains a little mysterious.)

Some it's love at first sight (hear), others it takes a few listens for it to grow on me, and then there are those I can't stand from the get-go.

When I first heard Captain Beefheart, it sounded like Frank Zappa and the Mothers on acid. I figured that out in five minutes. 

Some of my favorite artists I love the music right away, but can take at least 5 or 6 listenings before I can even figure out what the song is doing.... 

To quote Beefheart, "When It Blows - It Stacks."

That is all ye know, and all ye need to know.