After Ann learns that Mr. Harrison is at her father's restaurant, she and Don immediately head to Brewster. When they get to the restaurant, they are both in different clothes.
Ann places a "person-to-person" call to Mr. Harrison, but then ends up talking with the maid. The operator would not have permitted the conversation if Mr. Harrison wasn't present to take the call.
About 10 minutes in, right after Anne and Don leave Anne's parents' house they walk into Anne's apartment. Once in the apartment door you can see on the left side of the screen, a hand reach in from the "hallway" grabbing the door knob and closing the door.