With Metabisulfite (both Na and K versions) the recommendation is to allow the surface to drip dry before allowing contact with the wine. It is the vapor that comes out of the liquid more than the liquid itself that is effective at sanitizing the surface.
The manufacturer of Star San recommends 30 seconds of contact, though it is my understanding that there are only a few uncommonly encountered infection microbes that actually take that long to die when hit with Star San. For all practical purposes, you can consider it to be instantaneously effective.
By the way, if you decide to go with sulfite, you are better off using the Ksulfite. The NaSulfite can impact the flavor of your wine.