I usually put my corks in a clean plastic colander that rest on the outer top rim of a 2 gallon plastic bucket. I pour ~ 300ml K-Meta on top of the corks and the solution runs through to the bottom of the bucket. I place the lid on top and then go about finishing getting ready to bottle which can take up to an hour.
Thats probably way over kill as far as time. But it doesn't hurt. I would think 10 min would be enough to gas them well.