K-meta and sorbate are used to "stabilize" the wine. The k-meta is an antioxidant and preservative and the sorbate prevents yeast from reproducing.
I use k-meta at every other racking, but I only use sorbate if sweetening a wine. If your wine is finished, and you're not sweetening it, you don't need the sorbate. I try to avoid sorbate when possible, as it does have a slight taste that I find disagreeable.
K-meta should not be allowed to dissipate before bottling, as the point of using it is to protect the wine. If you're not sweetening the wine, you can bottle immediately upon racking into the sulfate/k-meta.
Broken Leg Brewery
Giving beer a leg to stand on since 2006