Continuity mistake: When Will escapes the party with Sylvia as hostage, he barely avoids an accident with an armoured car, into which the Timekeeper Raymond crashes. As Will leaves the scene, he is driving on the left side of the road. The camera shifts to Raymond for a moment, then back to a rear view of Will's car, now driving on the right. The camera angle changes again, and he is once again driving on the left. The right is the 'correct' side of the road, evidenced by all the traffic around them.
Continuity mistake: In the scene where Will is eating at the hotel, Sylvia is in the background. Several times her position changes oddly, but a second or two between shots technically makes the changes feasible, if implausible. Towards the end of the scene, though, between angles her position changes from her head looking down, with her bodyguard 10 feet away, to her head straightened and the bodyguard beside her.
Continuity mistake: When the Timekeepers Police car is sideswiped by the truck, you can see the drivers door bursts open, and the panelling where the door would latch onto to close is dented severely which would prevent the door closing again, but when the camera cuts to an inside shot of the car, the door is shut as if there is no damage.
Continuity mistake: When Henry Hamilton dies his body falls directly down from the bridge, but when Will sees him from that same point on the bridge, the body is now roughly 50 feet from the base of the bridge. Additionally, his body splashes, and then 'bounces' back up, as if the river were at least several feet deep - but when Will looks down, Henry's body is in mere inches of water. And the current was flowing towards the bridge when he fell, but when Will looks down, it's flowing in the opposite direction.
Continuity mistake: Justin Timberlake drives over a spike strip which leads to losing control of his car and falling into the LA River under the 105 Freeway bridge. After Timberlake and Amanda Seyfried awaken, Amanda walks away from the wreckage and the tires on the wrecked car are still fully inflated and supporting the weight of the car.
Continuity mistake: SPOILER ALERT: When Henry Hamilton is first visible through the window by Will Salas he is sitting on the bridge and located on the very center. This bridge is the 7th Street Bridge in Los Angeles, which is a three arch viaduct design. After Will runs outside the building, the camera cuts back to shot of Henry, who is now sitting over the west bank of the river. The next shot, Will is directly in front of an electrical utility tower which obviously would never be placed over the center of the river. Then a closeup with Will's feet visible where you also can see the east-side arch and that he is still sitting over the west side arch of the bridge. Then when Will falls off the bridge he is back over the center arch of the bridge. It's most likely that the movie crew needed to relocate "Henry" to the west side in order for a camera boom to reach him for the close-up shot from the ground.
Factual error: Spoiler alert - When Will's body is recovered under the 4th Street Bridge in Los Angeles, the 6th street bridge and the 7th street bridge (the one that he fell off) are each visible in the background. Meanwhile the water is visible moving towards the 7th street bridge which indicates that his corpse floated against the current.
Other mistake: At the end of the film, as Will and Sylvia run from the time mission after giving away the million years, they run out of downtown and towards the border of the Zone. Raymond drives to that border, gets out of his car and runs towards them. The area is a desolate, empty road, with no buildings or other obstructions to the view - one can see miles across the landscape - yet Will and Sylvia don't see Raymond running towards them until they are within 50 feet of each other.
Continuity mistake: When Will and Sylvia's car hits the stingers (spike strips) that blow out the tires, they are driving on the 'right' side of the road. Off the edge of the right side is a grassy area. Will veers to the right trying to stay in control, then the camera angle changes, and we see he is on the other side of the road veering left, where the concrete river is. The camera angle changes, and they are back on the right side, just before another angle change where they fly over the edge... Of the left side. Perhaps there was originally a wide shot showing the car veering way across the road and back; but in the final edit, what we see is a big continuity mistake.
Continuity mistake: When the Minutemen's trap crashes Will's car, they check Will's time and say "he's got minutes. He'll wake up dead." This tells us he has very little left. When he escaped the party the night before (so this is perhaps 10-12 hours later), he had just 2 hours on his clock. Additionally, Sylvia wakes with just 32 minutes, and Will is still able to share some time with her. Yet he gives her only about 4 minutes.
Continuity mistake: When Will leaves Dayton for the first time, the car leaves Zone 12. Later it goes through Zone 8, and eventually arrives at Zone 4 (New Greenwich). But when the authorities are first checking the security footage of Will on the bridge, they have a Time Zone map on the wall, and Zone 12 and 4 are next to each other, with Zone 8 in a different direction.