EDIT: I withdraw this suggestion, based on the info in the replies I got below.
Has anyone tried to walk over rough terrain or the wilderness at midnight with only whatever light the moon gives off? It is incredibly hard.
In my opinion, for realism, the player should suffer a penalty for travelling at night. Currently, in the game he can see everything from a hilltop: every feature of the map like rivers, lakes, villages, etc. and travels through the forest easily. Go to a forest at midnight and try to walk through it, you can see almost nothing. Now try to walk through a forest *not on a path*, it's not only very dangerous but it will take you 10x longer.
So my suggestion is at night to make how far the player can see on the overview map to far less, e.g. 3 tiles, and if walking through a forest it should take 5x more time and fatigue.
What does everybody think?