I guess most of my evidence for this is just that bit in the series of flashbacks in episode 35 where we see the Regent tell the palace clerk that Ye Zun (still trapped in the Pillar) has been "stirring" recently. He seems displeased about the situation, and adds: "Ten thousand years ago the Black-Cloaked Envoy worked hard to make this refuge viable. I can't be the one to ruin that with my old man's inefficiency." I'm guessing the siege took place shortly after that?

I'm not sure that works, since the episode with the Shadow Man from episode 1 had already happened prior to the siege? The flashback was around the time Shen Wei woke from his dirt nap.