Note that I am talking about magic armor, if I want to stack armor I can go much higher. And 150 was the bare minimum to get my game plan to work in the last encounter where I only really have to worry about Alexander (and even then it's a minor inconvenience).
So it takes about 2-3 mobs to take down all the armor within the first turn assuming they happen to focus fire that target. If they don't then it'll take 2-3 turns or more to get rid of it. The general duration of combat is about somewhere between 2-3 rounds.
Instead of time, I would propose we look at the other resources it takes to get rid of that armor (magic or physical) and what are the consequences of failing to do so during the first turn really means. When combat lasts for such a short duration it's hard to quantify something as 'quick' without looking at resource expenditure.
