17 CFR §100.1

A period of seven business days is required during which contracts for future delivery in the current delivery month of wheat, corn, oats, barley, rye, or flaxseed may be settled by delivery of the actual cash commodity after trading in such contracts has ceased, for each delivery month after May 1938, on all contract markets on which there is trading in futures in any of such commodities, and such contract markets, and each of them, are directed to provide therefor.