The latest update of the game (version 1.1.3 from September 2011) has added a new Day and Night Feature.
This feature can be enabled or disabled in the Options Menu (Main Menu à Options à “Day/Night On” or “Day/Night Off”.
When the Day and Night is enabled, the village (as well as all of your neighbour’s villages and random villages) will get darker and darker until, at midnight it has gone completely dark and the lights in the villages are glowing.
At the moment this feature is not tight to the devices current time, but to PST (Pacific Standard Time). That means, depending on where you live, it might be night in your village even though it is day outside. Hopefully this will get fixed soon.