Forty-eight hours is more than enough.  

Wish there had been a forensic investigation.  

But given what we already know--as opposed to what we guess--it is apparent why there wasn't one.  

It still puzzles me that people aren't bothered by the lack of an investigation.  

Thinking further, the elevator core seems the right way to do it:  Start the collapse in the core to make the debris fall inward and pull the outer-wall support members in after.  The central collapse has to stay just ahead of the collapse of the outer columns and skin.  

Explosives in the elevator core would explain the great fireball in the elevator shaft that spread across the first floor, which at the time was attributed to burning jet fuel.  (I forget which tower this was.)  The problem with the jet fuel proposal is that--while it cannot be dismissed outright--it does require a lot of fuel to quit moving forward and stop dead, get funneled into the elevator shaft, and then fall down all 70 or 80 floors--in fine burning droplets that aren't too fine to make it down all the way down.  Not sure it's impossible, but if 9/11 really was done as a demolition using the elevator shaft, the fire-ball is straightforward and obvious.  

The Fates are kind.