Assuming you are referring to the classic Noxzema deep Cleansing Cream, the answer is three to five minutes.
Noxzema was created over 100 years ago and has been a staple in American medicine cabinets ever since. The deep Cleansing Cream is meant to be used as a mask and should be applied to clean skin. The directions on the Noxzema website say to leave the cream on for three to five minutes before rinsing it off with warm water.
This deep Cleansing Cream is unique because it contains a mixture of menthol and camphor. This combination gives the Noxzema its signature cooling sensation. The deep Cleansing Cream is also supposed to help with acne. The camphor is a natural anti-inflammatory and the menthol has a drying effect on the skin, which can help to dry out blemishes.
So, if you are looking to try the classic Noxzema deep Cleansing Cream, make sure to leave it on for at least three minutes (but no more than five) for the best results.