No. I know the same problem you're going through. What you need to do is set the that time to like an hour ago, a month ago. Etc.
So you'd want something like this: setcookie("visitor", $login, time() - 1400);
I think that would work nicely. Destroying cookies is impossible, the only way to get rid of them is to set their dates in a time that isn't now ;-). Tada, done.