It’s exactly how it sounds. You complete all “Song Easter Eggs” in the Zombies mode as fast as you can. Going in order from “Nacht der Untoten” to “Der Riese”, where the timer starts once you gain control and ends once the activation sound is heard on each level’s Song Easter Egg (Timing would be in Game Time).
If this does become a category I stongly suggest either banning the Nacht der Untoten “Help door” wallbang or making a sperate category allowing it.
Here is a run of “All Songs” in 9:08.848 that I archived showing that this category is indeed a working category that could be added to the page as the first full game category.