How long should I leave the face mask on?

I'm planning to use a face mask to take better care of my skin.
But I was wondering how long I need to use the mask pack to make it effective.
My skin type is oily, and I tend to have acne and large pores.
Generally, how long should a face mask be used to have a beneficial effect on the skin? Will using a face mask for a longer period yield better results?
Or would it actually be more effective to use it multiple times in a short period?
Also, I would like to know if the usage time of the mask pack varies depending on skin type.