Do the Time Echoes ignore stealth (ala Rularuu Eyeballs) with normal aggro radius, or have built-in increased perception or a power that increases their perception (ala Snipers) which extends their aggro range?
Sleepykitty added this note to their page:
All Time Echoes have sniper range aggro and can see invisible players when near them.
However, Sera404 verified that Superior Invisibility, at least, snuck past them, which pretty much discounts the "ignores stealth" part of the question. Superior Invisibility may be a higher stealth radius than their perception, though.
I can't get in-game to verify this with a Power Analyzer (http://paragonwiki.com/wiki/Temp_Power:_Power_Analyzer_mk_III) and they don't exist in our current CoD information (outdated by several issues).
I know the Time Echoes in the last mission definitely do not have any +Perception, but they're all minions & Lt.s
The Time Echoes in the first mission are all AVs and AVs do have some +Perception.
If they had sniper level +Perception, all of them around the Ouroboros pool would immediately see you upon entrance and fire... and that doesn't happen.