Songs are "supposed" to be three and a half minutes long. Frank Ocean's Pyramids is nearly ten minutes long.

Films are "supposed" to be 120 minutes long. Martin Scorsese's Irishman is 209 minutes long.

Paintings are "supposed" to be pulled from a palette of 10 to 20 essential colors. Mark Rothko's Orange and Yellow pulls from just three.

Novels are "supposed" to be 120,000 words. Ray Bradbury's Fahrenheit 451 is 46,118 words.

Rules in art aren't so much rules but suggestions. They should certainly be considered but they don't have to be accepted.