Sometimes out of spite for the game, I'll sit around at 1 hit point with some life regen waiting for the 23 million poison damage from hell unravellers or spiders to wear off. It seems to me I can wait indefinitely because it stops causing damage at 1 hp? If I chug a belts worth of super healing potions, it seems to wear off faster. Is this just my imagination? I'm guessing the duration is unrelated to how much life it takes?

It is unrelated. Its duration has to wear off. It doesn't kill you, you always stay at 1hp. However, the next hit will, even if it is poison again.

Mind also that in hell the poison duration is higher. Just like resistances are lower.