Time allowed for a Buyer to return an item with no return policy & case opened

[blizzard-n-may]

Hello,

As a Seller, I had a buyer who proceeded to want to return an item to me.  I have a no return policy in place, and with that said, believe the buyer acted less than truthful for reasons to return.  With  a Case opened, my main question is this:  how many days does the buyer have to return the item - specifically how many days after case opened that Seller is to have said item?  I realize there is a 6 day limit for a Seller to issue a refund to a buyer for a return, but I am curious as to how many days is the limit for the Seller to receive the item back in my scenario?

Thank you.