They should have offered Stosur/Kerber the option of playing after Ree/Caro. If both agreed it was ok to play so late, that's how it should have been scheduled. If they disagreed then the USTA should have made the call as to where and at what time they would play. If the mens's doubles needed to be played on Ashe, that could have taken place after Kerber/Stosur. After all it is Saturday night, a lot of tennis fans would have stuck around.