Corrected entry: In the opening shot of Union Square from above, all pedestrians have very long shadows. Later we learn that the action took place during the lunch hour. The sun should have been higher and the shadows shorter.
Corrected entry: Gene Hackman's character has been listening at the door of Terri Garr's apartment. When he finally enters her apartment and she tells him she feels like he's somehow listening to her, the boom mike is visible in the frame in several shots in the scene.
Correction: I watched this scene several times watching for a boom mic to appear. Never saw it. I think what you saw was the top of the door frame. There is a conspicuous reflection there that could be mistaken for something entering the scene from above the frame. But it's not a boom mic.
Corrected entry: Throughout the movie when Gene Hackman listens to the conversation on tape, the man says "He'd kill us if he has the chance," with no emphasis on any one word. But at the end of the film after the murder, he thinks back, and the man says "He'd kill US if he has the chance," stressing the word "us." That totally changes the significance of the sentence. If it was used throughout, it would have been easy to guess the twist at the end.
Correction: Harry sees (and hears) things in a different way than others. He probably was so paranoid about causing another murder that he heard one word being stressed instead of another. Indeed, the film also seems to be about how people perceive things differently.
Correction: The shadows in the scene are pointing nearly North, actually just east of North, Indicating the time is roughly about 1:00pm. Also, based on the length of the shadows and the clothing people are wearing, it appears to be winter. There's no mistake here.