K-meta is added to the primary to stun any yeasts/bacteria in the initial must. Wine yeast is pitched a day later after much of that K-meta has dissipated.
Different folks, different processes. Many people transfer the wine to a secondary vessel (carboy) while the wine is still fermenting (say sg around 1.005). Do not add K-meta while the wine is still fermentng. While it may not cause problems, there is a chance that the added K-meta will cause a stuck ferment. Certainly, there is a good chance that the K-meta will slow down the ferment.
Once the ferement is finished, K-meta is added to help prevent oxidation. In a properly sealed vessel, this K-meta will not dissipate like that added to the primary.