SQL Job Archival Process Clarifications
They are meant to do a check on each node to see whether it's the primary or not before continuing to run the rest of the logic but they didn't bother.

It sounds like someone set it up under the belief that it will never interfere with each other concurrently (maybe because it has file locks or something else). 

No biggie. If you're redesigning it I would add the primary replica check anyway. The question about 30s to 5m is impossible to say though. It's not going to break the AG but what it does to the software is another question.