When the WTC was bombed in 1993, it took about 6 hours to evacuate. The elevators are out and you have to stream tens of thousands down stairwells. My heart hopes you are right, my mind tells me the number of deaths and casualties will be very high.
The difference between '93 and now is most of the power for elevators was in the lower levels and the smoke was going up.
This time the damage was up top and the elevators are compartmentalized, the towera are essentially three buildings stacked on top of each other separted by Sky Lobbies, in this case it is conceivable that the two lower sections were usable and the smoke problem is not as bad. I hope as many as possible got out, but I wouldn't count on it!