"What a Difference a Day Makes" - As Meredith, Derek and all of their friends prepare for the big wedding, a group of college students, injured in a car crash as they were heading to their graduation ceremony, is admitted to the ER. Meanwhile, Izzie fears the worst when she begins experiencing familiar symptoms, on "Grey's Anatomy," THURSDAY, MAY 7 (9:00-10:02 p.m., ET) on the ABC Television Network. (ABC/SCOTT GARFIELD) ELLEN POMPEO