Short Duration?
http://wiki.project1999.com/Spirit_Quickening says 1 hour. I always keep Spirit Quickening up on pet, because it's only 50 mana and lasts 1 hour. I typically then cast Celerity on top of that, and only use SQ for the AC + STR buff. Granted the haste is only 20%, but if I'm lom it's better than nothing.