How could they have known that ahead of time unless al Qaeda call and tell the DOD that the attack was going to last a certain number of hours?
For all DOD knew, the attack could have continued for days.
I mean, it's as silly an excuse as saying that certain units weren't deployed on D-Day because they couldn't have gotten there before the coast was taken.
Ahead of time, how the heck do they know how long an attack is going to last?
They don't. This statement could be a hindsight thing, but that's as useless to the KIAs as an Obama promise.
It's like a fire department not responding to a house fire because they believe the house will be consumed before they can get there.