So, when does Leaverbuster trigger?

I've had some bad luck with connectivity recently. About two weeks ago, while messing around in a Bots game in a coffee shop, I got hit with unplayable amounts of lag about five minutes into the game which led me to cross the street to a library to continue the game. I returned after about ten minutes of being AFK, but was still warned for leaving. Then, a couple days ago, my block lost power during a ranked match, causing me to leave after only about four minutes into the game.

I've not yet been punished for this, but with two leaves in only a few weeks, I'm a bit paranoid about what my current status is, especially with bad weather headed my way this week. Does anybody have hard numbers for when Leaverbuster kicks in? The official page is fairly vague about it.