You can add it right after adding both k-meta and sorbate but I like Tom like to wait at least a few days to make sure these 2 agents have dissolved and mixed in thoroughly so that you dont have a re fermentation.
Thanks a bunch Tom and Wade. This brings another question. So, I already added k-meta about 2 weeks ago b/f I decided to sweeten the wine. I wont have to add that again will I?
Not until about 3 months after you added this unless that last time you used it was before fermentation as fermentation will generally burn most of that sulfite out of your wine.
If your wine has fallen clear, racking it will also remove much of the potential to ferment. Some of the yeast that are in the lees could be still living and capable of fermenting even if the sorbate keeps them from reproducing.
Agree with above - wait a few days before backsweetening and since you already added the k-meta in - you will need to add more every 3 months of bulk aging.