Silly question, is this in a song or link category?
Songs are subject to lots of rules, (like cant play the same artist within xx hours - especially if you have all the stories labelled as the same Artisit i.e. "Short Stories") links are not and can just rotate around the decks evenly.
If it were me, i'd have a Short & Long link cats, and then place those in the clock where you need them, if you place them an even number of times in the clocks - have an odd number of items in the category so they don't come up in the same time each week.
Broadcast Radio Ltd