As of the latest content and patch on Book 7 I believe now he may spawn during the day. While doing my GRD Snow Beast deed I came across him in the afternoon after starting to clear the area around the 'noon' in-game. He was sitting at the 'U' in Bruinen in the North Bruinen Source.
Snowback only spawns at night! If you kill his placeholders, you can kill him once ever 15 minutes or so. But once dawn breaks, take a break for 3 hours or so, because he won't be back until night.