As title said.

In my most recent playthrough, I turn one of the Fallen empire into clusters of ultrafractured world. My attentions were occupied elsewhere, so I didn't notice how long it took them to turn from unstable world to stable one. (Stable, as in "colonisable", not "the place where you keep the horses")

So, a while later, I turn one of the world in a very beautiful location into Unstable Ultrafractured World through "Final Order" decision, hoping to turn it to Void Sphere and turn it into my new capital. Problem is, it's been a while (at least 10 years, I think), and the world still haven't stabilized yet.

So, how much longer would it take for it to cool down and let me start colonizing it? Or does this has to do with the world become ultrafractured through decision rather than orbital bombardment?

Thanks for any help in advance.