I understand you, I too want to save Chaos Aliens, but if Long Founding is anything to go by, any time skip will happen only after the Fifth Turn. Guilliman got stabbed only after we were done with Keepers of Truth and started doing Eternal Guard. It was also after the Fifth turn that requests started being inactive and unavailable, mainly Xenocide request.
So we still should have time to protect Sessetium after this turn, and we already done a request for "practical" reasons, the Mining one, I think we should now do something for fun, after all, this is the whole point of the quest.