Not familiar w/Skyrim but -
---there's a mild bell sound when he spawns. He spawns some distance away and there's a brief moment/period before he starts "hunting" you giving you time to bonfire or escape other ways.
---there's no specific event/timing re: his spawning that I can tell. You go beyond safety zones/warded bonefire at night and maybe you'll get to explore a fair time, or maybe you'll hear that bell/see him spawn in really quick.
---you'll see him/hear the bell in Act1, but he just appears on the edge of visual ranges then fades away - he doesn't start hunting you until you've reached Act 2
---he scales I think, but skills/gear + the slow time Arthur skill as a leadup would eventually make him manageable. BUT he's immune to a lot of magic (frost, fire I think). Or maybe you could get him stuck on terrain and cheese him.
---if you manage to kill him before dawn, it's maybe a few game days before he starts up again.
Edit: his purpose is to prevent players from excessively "farming" things that only drop at night, plus (I assume) just to annoy and present a skill challenge.