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: 15 Minute APA, Simple Cyser '14 (Nelson Sauvin Dry Hopped!), Spiced Cider, Spur of the Moment Graff
Primary: Simple Cyser '15
Secondary: Why do I keep this line here...?
Bulk Aging: Cocobochet, Wild Cider (2014 & 2015)
Planned: Fruitcake Old Ale, Not Just for Breakfast Stout. Otherwise, so many ideas, not enough time to brew them....