Costco's move to extend operating hours this summer is paying off big. "We estimate these incremental hours added about 1% to weekly US sales since implementation. This has been very well received by our members," CEO Ron Vachris said during the company's fourth quarter earnings call Thursday.The company beat expectations with full-year revenue of $269.9 billion, or 8.1% over last year. CFO Gary Millerchip also said that the extended hours and other new perks led a higher share of shoppers to upgrade thei ...