Adding K-meta and K sorbate generally will not stop an active fermentation, only prevent restarting. Generally they are best used after your fermentation is complete and the yeast dropped; the additions allow you to add more sugar to backsweeten without fermentation kicking back up. As a rule, I would say you don't even need the additions if you're not planning on backsweetening...once you've reached FG, and it's stable for several days in a row, you can package it. Forgive me if I'm stating the obvious, but I would also note that if you do add metabisulfite and sorbate you will not be able to bottle carbonate...
Packaged: Vienna Simcoe SMaSH, Mayan Stout, Caramel Quad, Basic Spiced Cider, Spur of the Moment Graff
Recent Meads: Cherry Melomel, Belgeglin, Bochet
Primary: Fresh Simple Cyser
Secondary: Why do I keep this line here...?
Bulk Aging: Mead Day '11 Ginger Metheglin, Cocobochet, Mead Day '12 Traditional (orange blossom) Mead
Planned: Hop Metheglin #3 (NZ hops), Trad. Gesho T'ej