when this was first available as a timed mission, NPCs didn't have an expiration timer (and I was outgunned by the ships that stood between me and the ships I needed to kill for this mission) Now that I have it as a normal mission, it appears that the randomly ranked Zolazin (I'm at rank 112 and getting rank 10 NPCs) still don't have a timer. Are these guys supposed to stay on forever, or did Dan miss that?

They are a mission NPC so they will not have a timer. The truth is you want them to stick around so you can kill them. Which I did make my #1 thing to do. I am done and now I will be seeing croshifters show up the same way here and there. Same thing no timer, but I want them to show so it does not matter.

chron shifters are also mission NPCs though and they have a timer. And like the chron shifters, these zolazin ships I'm talking about randomly appear on your battle screen when you have the mission available and drop the item needed to progress in the mission. If these ships appeared as a reward for mission completion like the crimson shriekers or shroud bases I'd understand them having unlimited time to finish