Manufacturer instructions for the Ninja Creami say you must freeze for at least 24 hours. That said, so much will depend on the temperature of your freezer and the composition of the ingredients used. Many people cut it a bit short and have good results. The Ninja Creami will drill at the intensity of the setting you select whether your mixture is completely frozen or not. There is a risk behind drilling a lesser-frozen mixture with less resistance than a fully frozen mixture. Theoretically, this could damage the machine. Each time you run a spin, the ice cream gets softer and softer. If your ice cream is not 100% frozen throughout the entire pint (it's very hard for you to tell what's going on in the middle of the pint just by touching the top), it can go from hard to soup in one spin. That has happened to me after an 8-hour freeze before.