I just got out of a game i finished where i played at night for the first time. Played for about an hour, and only pulled one zombie. I don't know if the zombies is affected at nighttime or not, but i find nighttime much easier than daytime. The tension is also much higher during nighttime because I can't really see much. Didn't find any weapons except an hatchet though, searched three or four barns and three deer stands, so that was kinda unlucky. All in all, i find the lack of vision improving the game, rather than breaking it.