Still in R166, but I never noticed it for the day/night transition, just for lighting campfires. As a result, I think that maybe the day/night transition flash also is related to the lighting, as in the video in the OP, that’s when the lights I had placed in my town automatically lit up. The light flash around a fire or lamp seem to be local, but maybe the effect appeared global because I had lamps spread all over my town.
Examples at approximately 5:44, 6:51, 7:27, 14:11.