The world's largest retailer says day-after-Thanksgiving sales will begin at 5 a.m. Nov. 27, but most U.S. stores will be open 24 hours to prevent a mad dash. The announcement doesn't affect most of Wal-Mart's Supercenters, which are already open 24 hours.

Federal safety regulators cited Wal-Mart for inadequate crowd management after the Nov. 28, 2008, death of a temporary employee at a Long Island, N.Y., store. A crowd of shoppers broke down the store's doors, trapping the employee, who died of asphyxiation.

.