Timer on raid boss

How would this work for bosses that don’t have the regular style enrages (aka boss gets big buff) where you get overwhelmed with aoe damage until you die or the boss dies, like Inerva or Denathrius? Or bosses that just instantly 1 shot you if you don’t meet the enrage timer, such as Stormwall Blockade back in Battle for Dazar’alor, or Il’gynoth in the Emerald Nightmare (these also go through immunities).