Yeah well, right now you have the choice to play on a "daytime" server or normal ones. I still think that the idea to sync in-game time with real time is a good idea, but I can't stress enough the need of dynamic shadows for that matter. Fortunately, this feature is planned with the coming renderer (bohemia said that it will be implemented in Q1 2015). And when this time will finally have come, playing dayz in night time will be really really fun/spooky and give a complete new type of game experience.