What is the rule of thumb for petitioning bards on zone monopolizing

[wimlin]

Title says it all. Seriously at what point can I petition it and have a GM make them stop taking every mob in the zone for a 30 min AE kite. It says it in the rules, but I want to know when its ok to petition it. Is it a certain number of mobs.. do I need to time how long every spawn is gone for? The rules seem to say you can't monopolize a zone, but what is the definition of it?