Poison cleansing totem should last you the whole fight. It has a 5min timer like all the others, or am I wrong? Thought really the only ones that had a timer shorter than 5 where the grounding, tremor and some of the fire totems other than wrath. No need to stagger them one should be sufficient, like one of the other posters said if it is really an issue then spread them around a bit further so that they dont get all hit by the poison but still use the poison and nature totems on this fight it is a must.