For me I will always remember it when it stood. the plaza has like 50 mph winds/gusts and the underground mall was huge. You could walk forever underneath there to avoid the wintry weather above.
On that date my wife (pregnant at the time) and I were living in NY but I was working in NJ. I was surprised to hear on Z100 about a "small plane" had hit the trade center and thought it was hoax - but switching channels to 1010WINS I realized this was serious. In the end by the time I arrived to the office, we had all gathered at first around the PCs to check the newsites (but then we got 404 errors because of too many hits to the site) and migrated to the cafeteria to watch TV. We were told the bridges/tunnels would be closed and my coworkers were trying to find hotels/places to stay in NJ. I guess I was crazy but I said I had to be home with the wife. A catastrophe like this and I just wanted to be near family - not holed up in some hotel in Morris Plains.
I drove all the way up into NY via the Tapanzee and found myself one of the few vehicles driving south on I-87. Most of the ramps/exits were starting to be blocked by police vehicles and occasionally a EMS responder would go blasting by me going 90 on I-87. Needless to say I was a little freaked. Everyone is trying to get out and I am trying to go in to be with my wife.
I was forced off I-87 by a roadblock of police vehicles in the Bronx. I drove around to see dozens of vehicles/18 wheelers all stacked up around I-95 cross bronx/ due to the closure of the GWB. All during this time my cell was pretty much useless and I was in a panic around what was going on.
I finally found the 3rd avenue bridge and got into Manhattan that way (weird how the police didn't stop that). I'll never forget as I rolled down the window asking someone for directions to Manhattan and he yells "YOU ARE IN MANHATTAN!!!". It took me only 4~5 hrs driving but I had finally made it.
I found the streets of (uptown) manhattan to be virtually deserted. The usual cavalcade of taxis were all gone. The eery smoke coming from the towers could be seen as a plume from uptown. I went into my apartment finding my wife. There's more to this story here but i'll skip it as there were some "people" who couldn't get back to NJ that were staying at our place.
But those 24~72 hrs are just something that I will never forget.
I salute all of you who are first responders or have family in those professions. It's a privilege to know there are people who are willing to sacrifice so much for the safety of others.