Near the beginning, when the three main characters are seen as civilians, it is 1920. However, Otto's car "Baby" is a 1923 Voisin, and in the road race, the other car is a 1929 Renault.
After Erich and Pat leave the bar after their first date, a moving shadow of the boom microphone can be seen on the walls of the buildings behind them, following them as they walk down the street.