It depends on why you're using the campden to begin with!
For some recipes, you use unpastuerized fruits or juices so you use campden at the outset to kill wild yeast and bacteria that may be on the fruit. After that, it's used at every other racking (to keep the sulfites at roughly 50 ppm) and at bottling, as an antioxidant and preservative. If the sulfite is added to the wine, then it can't uptake oxygen and it "blocks" oxygen from binding with the wine. When it's bottled, the sulfite works as a preservative for the wine so it can be aged. Also at that time, sulfite (campden) is combined with sorbate so that the wine may be sweetened. This is called "stabilization".
For the recipe you mention, it uses already pasteurized juice I believe, and the wine isn't meant for aging, so sulfites would only be used if you wanted to use them as an antioxidant or as part of stabilizing the wine before sweetening and bottling.
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