[MistrNole]

The duration is determined by your target (Epic or Heroic). There are 2 parts to the spell - the stifle and the damage (2 ticks If i remember correctly), so the damage portion of the spell itself is fairly quick, most of the spell's duration is actually the stifle. True epic targets will have around a 2s spell duration for this spell, while Heroics will have the full duration.