You can go anytime. Or you can call up there.
You're supposed to wait while they process your books. You'll get more for your money by accepting store credit usually but they will pay cash also, just a lesser amount. You'll need to put your books to sell into their bins.
Any time they are open for normal hours of business.
The buyback counter is open during regular store hours, though it does close about an hour before the store (to give them time to value items before closing time). I have found that early in the week (Mon-Wed) is the best time to trade books in at Mckays. You miss the weekend rush, and they are generally more willing to take items.
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