As a skincare expert, I would not recommend leaving a foot mask on overnight. Foot masks typically contain active ingredients that are designed to exfoliate and moisturize the skin on your feet. Leaving the mask on for an extended period of time, such as overnight, can increase the risk of skin irritation or sensitivity. It's best to follow the instructions provided with the foot mask and adhere to the recommended duration of use. If you're looking for a more intensive treatment, you can consider using the foot mask for the maximum recommended time and then following up with a rich moisturizer or foot cream before bed.