The time required for a chocolate mousse cake to set in the freezer can vary depending on various factors, such as the size of the cake, the composition of the mousse, and the temperature of the freezer. However, as a general guideline, chocolate mousse cakes usually take about 2 to 4 hours to set properly in the freezer.
It's important to note that freezing times can vary, and it's best to rely on visual cues and texture rather than strictly following a specific time frame. The cake should be firm to the touch and hold its shape when gently pressed. To be certain, you can also insert a toothpick or a knife into the center of the cake and ensure it comes out clean or with minimal residue.
Keep in mind that it's essential to follow a trusted recipe that provides specific instructions for freezing and setting times, as different recipes may have different requirements. If you're using a recipe, it's recommended to follow the instructions provided to achieve the best results.