Wait. It despawns? Why?

That's not a good decision, IMO... At all. If one person's luck was really bad they could never see the instance. Possible? Not likely, but still. Maybe I'm annoyed I missed it because I was working, and I'll need to hope it doesn't spawn again while I'm at work.

I don't doubt I'll be able to see it, but I still think it's a bad decision to make it a timer to see the NPC.