"GREY'S ANATOMY - ""What a Difference a Day Makes"" - Bailey performs a test on Izzie as the imagined spectre of Denny Duquette watches ominously, on ""Grey's Anatomy,"" THURSDAY, MAY 7 (9:00-10:02 p.m., ET) on the ABC Television Network. (ABC/SCOTT GARFIELD) KATHERINE HEIGL, CHANDRA WILSON, JEFFREY DEAN MORGAN"