For Dirty F, let's use the Billiard Ball example.
Case 1
If we were to drop it from the same height as WTC1 in a vacuum (i.e. no air resistance) it would take 9.22 Seconds to hit the pavement. It would take a bit longer if we did include air resistance. Notice how the billiard ball speeds up throughout the fall
Case 2
‘Progressive Collapse’ in ten-floor intervals - Let's imagine that 9 out of every 10 floors were already damaged, and provided no resistance at all, so only every 10th floor is resisting the fall (very generous I'm sure you'll agree). Every 10 floors the collapse would slow down temporarily. Remember that no floor below the collapse can begin moving until the pancake collapse reaches it. In total the collapse would take a minimum of 30.6 seconds.
Case 3
‘Progressive Collapse’ in one-floor intervals - Now we'll consider the case where every floor provides resistance in the collapse. The time for collapse is now 96.7 Seconds.
Case 4
‘Progressive Collapse’ at near free-fall speed - If we were to start collapsing each floor below the 'pancaking' before the 'pancaking' reaches it. Here we get 9.22 Seconds! For the entire building to be on the floor in 9.22 Seconds, each floor below the 'pancaking' must start moving before the 'pancaking' reaches it i.e. it would require a detonation or destruction sequence.
Conclusion
The explanations in the 9/11 Commission Report and NIST are not physically possible, a new investigation is required