When Jimeno is dealing with the tourists outside the bus terminal, the shadow of the first plane is cast on the E Walk of The Westin New York at Times Square. This cannot be true, since both the E Walk and The Westin were under construction at the time and opened in October 2002.
During a scene in the hospital near the end of the film, a can of Sierra Mist can be seen on a table. Although this drink existed in 2001, it used a different logo in the 2000-2002 time frame. This logo is from the 2003-2006 time frame.
During an establishing shot at the beginning of the film, a Honda Element can easily be seen driving past an intersection. This car was introduced in 2003, so there couldn't have been one present in New York in 2001.
In the beginning, there is a view of the streets with a crossing sign. However, that type of electronic sign (the one with the hand for "Don't Walk" and the person for "Walk") was not installed until December 2001. At the time of the attacks, the old signs with the words were still in use.
In an early scene, Officer Will Jimeno has an Opie & Anthony WOW sticker in his locker, but the 102.7 FM logo in the top left is blacked out. This was taking place in 2001 when they still worked at that radio station.
In the scene with the local police going to Donna McLoughlin's house, a blue police car and a fire vehicle pull up. The blue police car has wheels on it only available on the 2003 and newer Crown Victoria, this movie was set in 2001.
On the bus scene, one of the officers got a phone call from his wife saying that a second plane hit the Twin Towers. Later on in the film when the officers arrive at the World Trade Center they look up at the buildings; there is no damage done to the South Tower. The report of the second plane hitting the Twin Towers could have been one of the many rumors going around, like when someone in the movie said that Israel had been nuked and was gone.
When Allison goes to the CVS with Jerry and Will's sister, her purse strap changes. When the camera is facing her the straps are both over her shoulder, and when the camera is on her back, one of the straps is on her shoulder and the other is hanging down. It switches back and forth between shots.
As Will is talking about his family, we see a shot of him talking with two rocks on his shoulder. However, after a few other cuts, in the next shot the rocks are gone. Then they are back on in the following shot.
As the bus is traveling to the World Trade Center, the route on the destination sign went from displaying a proper route message to a displaying a completely garbled message, and then returning to the route message that was displayed when the men boarded the bus.
There is a brief scene set in Hong Kong, where locals are stunned by what they see happening in New York on TV. The background clearly shows that it is daytime. However, when the 9/11 events occurred, it was night time in Hong Kong.
At the beginning of the movie, one of the characters asks the Yankee fan if he saw Jeter's home run during Saturday's game. Derek Jeter didn't play the Saturday before Sept. 11 because he was injured. In that game on Saturday, September 8 2001, the Yankees beat the Boston Red Sox 9 to 2. Enrique Wilson filled in at shortstop for the injured Derek Jeter and went 2 for 4 including a triple, with a run and a run batted in.
The scene outside the port authority building has a shadow of AA flight 11 moving over the officer from his right to left, which he followed visually, indicating a northerly flight path at that time of day as the sun would have been in the southeast sky. Flight 11 was headed south and at that time, its path was never between the sun and the port authority terminal, and it struck the north side of the North Tower.
In one of the opening scenes we see a #2 train, however this train is not a real #2 train. The real #2 trains run on the IRT line, these trains are characterized by being narrower, the train we see in the scene was probably a BMT line train; the BMT line trains look more like the one in the scene and also have a chassis as wide as the one in the shot.
There is an outdoor scene showing trees with leaves displaying bright fall colors. Leaves in the northeast US don't begin to change until late September and would not be at their peak colors until mid-October.
On the scene where the fire truck is driving down Broadway, the Engine Company number is listed as "99"; although the FDNY's highest "90s" engines only go to "97", this is not a goof - Engine 99 is featured in the FX network television show Rescue Me, and is making a cameo appearance here; 9/11 was a frequent theme throughout that series.
When McLoughlin and Kassimatis are driving to the WTC after the first plane strike, the sun is on the wrong side of the towers, in reality in the morning the sun is on the east side of the WTC, in the movie, its on the west side. This is corrected later when the other officers are shown at the base of the towers
On the scene where the police officers return to the police station and watch the news footage; notice that there is a cable wire stretching from the back of the TV to the ground, that's because the footage is rewound on a VCR from videotape not Live TV.