In my experience it shows up nearly every 2 minutes. Sometimes its a minute 50 other times its a 2 minutes and 30 seconds or so.
That's my biggest issue with the game. It's so incossistent you can't use a timer properly for it. And then when you do try to play, that monster can just randomly come and ruin your run. No warning, nothing. I was literally at green farmland thing and I heard him coming, even then I wasn't able to make it back to the house because of how fast the monster is and because of no warning. The removal of warning was definetly a mistake.