As a expert on the matter. I'll bet my first born and their first born and so on, that he hasn't coded for that much time. Remember Steam doesn't record active usage it just starts a clock when you open the program, the guy easily could've had the damn thing open during his streams and week with nothing happening. For example. I could tell you all that I've spent around 30 hrs in the new dragon ball sparking game. However there's periods where I've had to stop playing the game but don't turn off the computer. Sometimes for a decently long period. Mostly personal matters, I don't intend to power level here and say what. Point is I've have to do things that require me to give my full attention that I can't just turn off the game. The same goes for mald, whose very active in a lot of things but coding HB.
Safe to say it's not a literal time of how much he codes HB, but rather how much time steam has clocked him having Game Maker open.