From Mike Allen:

President Barack Obama will address a joint session of Congress on health care reform in prime time on Wednesday, Sept. 9, a senior official tells POLITICO.
Obama plans to give lawmakers a more specific prescription for health care legislation than he has in the past, aides said.
Congress technically returns to Washington on Sept. 8, the day after Labor Day. But many members had planned Sept. 9 as their first workday, so Obama is seizing the first moment when he will have maximum impact.
The address to Congress, the second since Obama took offiice, is a way for White House aides to achieve maximum news coverage as they kick off their plans to recovery from a disappointing August congressional break, which saw the president’s poll number fall as voices of opposition to health care legislation rose.
The exact time of the speech has not been set, but prime time ensures a huge viewing audience beyond the Beltway.