How does buying work — is there a “buy now”?

There is no “buy now”. Everything on the market is sold by auction in CRETA on Polygon. The seller sets a starting bid, people bid, and the highest bid wins when time runs out.

How long an auction runs is set for each collection, not by the seller. A new bid can extend the time. The countdown on the item's page is the accurate figure for that item.

These auctions are between users, directly on the blockchain. Creta is not the seller of resold items.