Typically, I let it run for a few hours at a time... clean it out every 2-3hrs... I typically fire it up after work ... clean it out once or twice and shut it down before I go to bed... 5ish hours at a time...
So I start it, run it for 2.5hrs... clean it... run it for another 2.5hrs and clean again... ready for the next day. If I do it on a weekend, I clean it out every 3-4hours... or when ever I remember