Is this guaranteed spawn once Ire message appears? That means it's not even worth staying in an area you're already in because of the 2-3 spawn radius. Seems like everyone should stop what they're doing and go to a unique spawn each time Ire spawns (Trav, Shenk, Eldritch, Summoner, Palace level 3, etc.)
You can stay in the area, unloaded tiles in the same area can cause the herald to spawn, and you can also stack up more than one ire at a time.
I have had 4 ires stacked up on my guy once before the heralds started to spawn, probably cleared 3/4 areas after the first ire.
The heralds usually spawn pretty soon afterwards, but I would not say guaranteed but definitely easier to spawn by loading in a new area.