me either I would like to know the original sources?
So exactly WHEN? Is there some sign that will give us at least a little bit of warning?
I think so: A farewell tape from Osama bin Laden, personally.
If OBL died slowly (kidney failure?), he almost certainly made a farewell tape. That tape will be played just before the attack. (He might not have if he died suddenly in a cave at Tora Bora.)
If I am right, then the arrival of a final tape from bin Laden will mean the attack is about to start.