"The window will open when the shuttle is on the ground," said Army Lt. Gen. Carter Ham, director of operations for the Pentagon's Joint Staff.
The space shuttle is scheduled to land on Wednesday at 2:06 p.m. British time at the Kennedy Space Center in Florida.
"All those who have a vested interest in this will then apply their best judgment as to when the best opportunity is to intercept the satellite," Ham told reporters.
The Pentagon said on Thursday the Navy would try to shoot down the satellite before it enters the atmosphere, using a modified tactical missile from a ship in the Pacific, to avert a potentially deadly leak of toxic gas from its fuel tank.
The Pentagon plans to use one missile, but also to have two back-ups. It will deploy three ships for the operation.