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Or is it an exaggeration, or perhaps a different level of perception of the battle? For me, it's simple: 3 seconds for a quick battle, 35-55 seconds for an easy battle where you only have time to defend and shoot, 1.5-2.5 minutes to kill a horde of zombies on level 11, and roughly 3-6 minutes to clear out monsters with 5+ speed and 6+ stacks. What you can do for longer, and more importantly, *how* you can do it, remains a mystery.