For me I have been trying to get to 10-15 sec then keeping 5-10 banked.
Also, I am having a hard time holding multiple mobs. I do fine most of the time, but there are too many times when I am waiting for keg smash to come off of cooldown and I am struggling to hold some mobs off of healers or dps (or generally just having good threat).
edit: Am I doing this totally wrong? Should not bank any other the the amount I get from one bok?