NORAD had 51 minutes from the first tower attack. There was plenty of time to intercept, attempt to negotiate, threat, and eventually make the horrible decision to shoot down #77. Mistakes were made. Hind sight 20/20 is an understatement.
And a tenth of a second is plenty of time to track, lower the bat, adjust your stance, and drive a 96-mph fastball into the parking lot. If you know it's coming, and you're one of the 0.01 percent of the population that makes it look easy. I'll scream at a player who whiffs at strike 3 in the dirt, but I know I couldn't do the easiest part of his job on my best day.
The FAA and NORAD, even after they were alerted that we were under attack, were faced with a scenario they had not modeled, had not practiced, had not anticipated. They had formidable assets to track and shoot down planes coming from international airspace. but who was planning to stop an attack between Wheeling and Arlington? And how do you pick out the threat from the tens of thousands of aircraft being tracked at the time?
Mistakes were made. Hind sight 20/20 is an understatement.
Okay, genius. Tell me what you would have done differently. Be specific. Which planes would you have sent, from where, at what time. Assume no information that the people who actually had to make those decisions did not have at the time. Even under those conditions, you have the luxury of having had five years to think about it.