The US AOPA website has an interesting animation courtesy of FlightExplorer that shows the flight paths of the aircraft involved. Go to
http://www.aopa.org/ to see it.
I'm curious as to whether it is possible to say, by looking at these tracks, when the aircraft diverted from their "normal" route of flight? That would presumably indicate when the hijackers took over, but not necessarily when the physically took the controls of the aircraft.