If you were keeping track with a thermometer, you would find that the temperature of water stalls at zero degrees Celsius for a bit — the exact time that the H20 molecules are rearranging themselves into the crystal structure of ice. Once the crystal arrangement is in place, the ice will continue to cool at a more or less steady rate until it reaches the same temperature as the environment in the freezer.

Source: Los Angeles Times January 11, 2019 13:02 UTC