During the car chase scene, as the car is rammed and begins to spin out of control, during the spinning, the pursuing police car is nowhere to be seen despite the 360 degree camera pan. It then re-appears when the car ceases to spin.
When Will is having breakfast at the hotel in New Greenwich, Sylvia is sitting outside a few tables away watching him. In the close-up shots of Sylvia, there is a guard standing directly behind her, but when the shot is zoomed out and viewed from behind Will the guard is either standing at the table in front of Sylvia's or behind the low glass wall behind her.
At the start of the film, the character Will Salas is seen getting out of bed and his time clock is on the left arm. Shortly after, he is seen looking through a window and when he turns to walk away, his time clock is on his right arm, switching back to the left arm after this scene.
The scene showing him turn away from the window is filmed in a mirror and therefore correctly reflects his left arm with the clock.
During the car chase, the leading car is rammed in the back with the inside view showing the heads of the characters in the rammed car being knocked forward. This is physically incorrect as, in an accelerating collision, inertia would cause their heads to move backward relative to the car.
The goof items below may give away important plot points.
After Henry gives Will all but five minutes of his own time, Will wakes up to see he has a bit over 116 years on his clock. He then gives a decade to his friend, buys some flowers for his Mom, spends years, as the timekeeper says, crossing time zones, and then gets a suit in a fancy hotel. Yet when he wakes up the next morning his clock still reads a little over 105 years.
In several scenes where Will and Sylvia are running, the heels of Sylvia's shoes shrink and grow in between shots. Most notably in the final scene where she runs into Will's arms her heels are several inches taller when she stands up than they were just seconds before. The strap on the shorter shoes is also further down the foot than the on the taller ones.
When Will looks out the window and sees Henry sitting on the railing, Will is forward, and to Henry's left. Yet when he runs to the bridge to try to give Henry more time so he won't die, Will runs up from Henry's right. This means Will either ran left out of his building to another bridge off in the distance, then back to Henry's bridge, or he ran across the water flowing in the drain without getting wet, across the railroad tracks, and up the incline to run across Henry's bridge - all in less than a minute, going by the time we see on Henry's arm.
Near the end of the film, when Will drives through a hail of police gunfire at a roadblock, the bulletproof window on the driver's side is down. A few seconds later, it is up, showing at least three marks where where bullets supposedly bounced off the glass.
When Rachel goes to get the bus to meet Will, she expected the cost to be an hour and had an hour and a half remaining. The bus journey must have been less than half an hour if it was to get her there in time. The distance was said to be a two hour walk. Will heads back towards Rachel when the bus arrived without her. If Rachel starts walking when the bus leaves and Will starts walking towards her half an hour later they will meet after one hour and fifteen minutes and she will have fifteen minutes left.