I haven't done anything scientific with it yet, but I would say it goes off as much as 20% of the time. If I'm not mistaken, I believe I have seen it trigger on enemies when a prior trigger was still in effect. This would indicate to me that it either has a) little to no cooldown, or b) my -recharge gear is reducing its cooldown. I'll try and pay more attention once I test it further. I imagine the information is somewhere in the editor as well, but I can't get IT stuff to appear in it. I extracted the database using tqvault, so perhaps it doesn't extract IT stuff correctly.
I will let you know once I know more.