First of all, as 'lag points out below there are a number of "Close Door" buttons on elevators that obviously work -- I've been in any number where you can close the door immediately after opening, so the "minimum open time" is bunk. Perhaps it's that way on construction after a certain date, but more often than not the Close Door button has worked when I've used it.

As for the Call Walk button, in my experience that is only meant to change things in times of low or no traffic -- similar to the street sensor that indicates a car is waiting at a light, the Call Walk button lets the system know someone is waiting to cross that intersection. So if there's no traffic, you'll still go through the regular cycle of lights -- whereas if the button wasn't pushed, the light wouldn't cycle through because there were no cars at the intersection.