Deliberate mistake: In the scene when the timer exceeds 38 minutes, said timer is displayed in big digits on a computer screen. There is a shot of General Hammond with the Stargate in the background. There is a pane of glass between the General and the Stargate. In the shot, General Hammond turns and looks at the gate, and then the camera's focus changes from the General to the Stargate itself. In doing so, a reflection of the timer in the pane of glass is also brought into focus. However the timer is displayed correctly when it should be flipped left to right as all text is when it is reflected in either a pane of glass or a mirror. On the DVD, the writers revealed that this was done on purpose so that the viewer would have a concept of the time running out even when the timer wasn't in shot. (00:17:30)
Continuity mistake: In a scene where Sergeant Walter Harriman tells General Hammond that SG-1 is ok, but Dr. Friesen is dead, Sergeant Walter Harriman is wearing the uniform of Major Davis (you can see "Norman Davis" written on left side of his chest). [His name was originally Norman Davis. At one point, Hammond refers to him as "Airman". This was misinterpreted as him being called "Harriman." Then, in the episode 2010, O'Neill calls him Walter. Thus, his name changed from Norman Davis to Walter Harriman. Still a mistake, but that's why.] (00:30:15)
Other mistake: When Thor reveals to SG-1 that the Replicators have reversed the time dilation device, he says time is moving at a factor of "10 squared" (100 times faster than real time). Carter says that in the hour that passed, 4 days have passed for the Replicators (which is correct), but then says depending on when they did it, hundreds of years could have passed. But that's not possible since that means years in real time would have passed. But the Asgard didn't set this trap years ago, just recently.
Other mistake: When Jonas says he has flashes of what's going to happen (and no-one believes him), Teal'c says they have encountered many strange phenomena but no-one who could see the future. Except Jack and Teal'c had a whole "Groundhog Day" episode where, because they were stuck in a loop, they could see the future. Carter then says it goes against all the laws of physics as we know them, despite knowing time travel and other things that break the laws of known physics exists.