The Min and Max values represent where you are in the hour, not how many minutes of music the fill should put in. So Line 3's fill targets the songs to end between :58 and :59 in the hour.
In this way, you can have items that get skipped if you ran over time. Imagine a situation where you have a prerecorded hour that varies from say 45 to 55 minutes. By putting a fill with min/max of :58/:59, you'll always end at that place in the hour no matter how long the item before it is.