potassium metabisulfite

Can we add potassium metabisulfite during third day of fermentation I mean primary fermentation

That's a bit late.

Or really early.

Should have done that before fermentation or after fermentation. Sulfites can stun yeast and cause a slow ferment or a stuck ferment.

Actually I use 20 minutes before adding yeast it but very small quantity 10 gallons and just 1/3 of teaspoon

Am I correct in assuming that you are using it to keep wild yeast and other micro organisms at bay during fermentation? If so, from what I've heard but I'm no expert, commercial wine yeasts are made to be more tolerant to KMeta and therefore 1/3 teaspoon per 10 gallons is likely to be okay. It may stun the good yeast for a bit but I imagine they'd recover just fine.

To be sure just call up the yeast company that you used. In my experience the support numbers for many suppliers like this have been very helpful.

Welcome to the forum!

I've never seen a kit or any 5-6 gallon recipe call for using K-meta during active fermentation. For fruit/country wines I see 1/4 tsp. k-meta being added to the must 12-24 hours before pitching yeast - I'm assuming for killing wild yeast.

The "engineered" yeast should quickly crowd out any native yeast in a good active fermentation.

Agroback said:

Actually I use 20 minutes before adding yeast it but very small quantity 10 gallons and just 1/3 of teaspoon

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What I normally do is add pectic enzyme first, 24 hours before anything else. Then I add the yeast. I let it ferment to dry (0.990ish) and then add potassium metabisulfite to stabilize. If back-sweetening, you'll need to add sorbate.

In all cases, the containers of chemicals have instructions on them as to how much to use.

The other thing that is really helpful is the More Wine Guide to Red Wine (or white wine if that is what you are making): http://morewinemaking.com/public/pdf/wredw.pdf

Since you only added 1/3 teaspoon for 10 gallons, I think you will be fine.