How long does darkness last on this the shortest night of the year in the Northern Hemisphere? It depends on your location. If you are far enough north, it stays light all night.
Here in Wisconsin (44 degrees north) the twilight ended around 10:45 PM and will return at about 3 AM. On the other hand, in a more southerly location such as Dallas the night will last longer. Twilight there ends at about 10:10 PM and returns at about 4:45 AM.
Farther north in Anchorage, the sun sets at local time 11:15 PM and twilight lasts until it rises again at 4:35 AM.