Chaos singularity's total duration is based upon all the other attributes, of which there are configurables.
for instance: Spreading out of the initial projectiles, increasing how far they go, or decreasing the speed of their spreading, increases the total duration, and vice versa.
the total amount of "attacks" the singularity has: increasing makes it longer, decreasing makes it shorter, also lowering the wait randomiser decreases duration, etc. etc.
The spell uses these as controllers, because otherwise the spell would get very awkward, programmatically.