Dynamic day/night cycle might not be really viable, (if doable) and hard to balance. Maybe just adding night/day versions of the maps?
If you can't see where you're going, yeah that'll be frustrating.
Although, if there were headlights, that could be interesting as well. Oh, oh, here's an idea, what if, there were quite dark, not pitch black, but dark maps, and you had to make a choice between using headlights to increase your ability to see for the cost of visibility, against not using headlights, lamps, whatever and hoping there is no building in front of you, with the ability to sneak up on people? That could result in some interesting gameplay. Maybe? :3