The time it takes to freeze water has too many variables to give a definite answer. Volume. Temperature of water before trying to freeze, temperature you are using to freeze, and the amount of impurities in the water.
It takes between 25 and 40 minutes to freeze the mixture used to make ice cream. On the other hand, water freezes at 32 degrees F and the time taken to freeze a certain volume of water will depend on the temperature setting of the freezer.