This will do it if the O.P. means 'fade to black' like he says in the post.
If, however, the question has to do with the screen dimming (on, but hard to see) then I don't think there's any way to alter how that works. It just happens whenever it wants to.
I'm also pretty sure I've seen it dim and go to black a second or two later, and I've also seen it dim and then wait a minute before going to black. I can't tell you why it changes.