Are there also limits as to the length of a song as it might pertain to being playable by radio stations? I've heard that there's some kind of magic number with regard to the length of a song and whether it's acceptable to get played.

The shortest rack I have played has been 52 seconds (Earsdon Sword Dancers)to illustrate a piece on rapper dancing prior to DERT in Liverpool, and the longest 13 minutes (Chris Woods "England in Ribbons"). I don't play a lot of long material but anything up to 5.15 and time is not a factor. But if I want to play something I play it without thinking of how long it is.

Then other factors come into play. (Like how long have I got left!!)