How do you use skin whitener cream?

Do you have to go to sleep in order for it to work or does it work either way?How do you use skin whitener cream?
I had a cream my dermatologist gave me. It was originally supposed to get the ex-pimple stains from my face, but it actually worked as a whitener, so I kept using it. I have no idea what was in that cream, the only thing I know is that is had aspirin in it. Also, there are some mask that work like that, may be the mask is even better... And no, you don't have to sleep in it. It just takes an hour, or two - max.How do you use skin whitener cream?
The critical factor is time - it is irrelevant whether you sleep or not. You might also want to consider why you want to whiten your skin, pale is simply not that attractive.