I usually define openers as being your initial wind up, and the burst that follows. That would place the end of the opener at the first Midare Setsugekka, about 35 - 40 seconds into the fight depending on your skillspeed. At this point you've got all 3 buffs up (Yukikaze, Jinpu and Shifu), used your potion, put up Higanbana, used Meikyo Shisui, Guren and Hagakure and you finish off with several Shintens and a Kaiten buffed Midare Setsugekka.