After some rather boring waiting to test it... A8, a.k.a. Brute Justice, on the normal difficulty has an enrage timer of 12 minutes, at which point it just smacks the entire party for instakill damage. That fight with an average group didn't take anywhere near 12 minutes even back during HW when every Job was objectively weaker.

The enrage timer doesn't make it harder, just makes it so that there's a failstate if everyone just keeps dying constantly.