I think we'll find that things were already in motion but that the information was still being disseminated when the Pentagon was hit.
My sister-in-law believes she saw the plane turn towards the Pentagon. She was sitting in traffic and thought it was odd that the plane turned toward her right. Normally, they'd have been turning the other way toward Dulles. If the plane was veering off from a Dulles flight plan, it would have reached the Pentagon in under 30 seconds.