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True, the night has to have something bad about it.

As for the game engine, this game utilizes Unity (as it states in the opening credits). I have UE4 installed, so I could try to figure out how to add a day/night cycle with that as an experiment, but as far as I know, most programs have confusing or complex ways to implement such cycles. I've never used Unity, though, so I'm not too familiar with its capabilities.