For instance: the power "Energy Twister" says it does 360% damage over 6 seconds. Does this mean it does 360% for 6 seconds, or 60% per second for 6 seconds?
Easily put, it means it does X% of damage over a period of Y seconds. Meaning to get 1s of Damage dealt, you have to do X/Y = [DMG]ps
P.S - For an afterthought, according to your example, 360% per 6 seconds, if it was 360% per 1s, that would be a total 2160% damage after 6s. Yeowch! (But overpowered much?)