Corrected entry: When Fredersen visits Rotwang to ask about the secret plans found on the dead workers, he looks at his watch and it is plainly a normal 12-hour timepiece whereas the futuristic city uses 10 hour clocks. This shot is from the 2004 restored version on DVD and is missing from the 1984 Giorgio Moroder version and possibly others.

Correction: The 10-hour clock in question represents a time clock that measures the duration of the workday/shifts (when the hands reach 10, the shifts change). It is not the time of day. A couple of times in the film, we see both normal 12-hour and 24-hour clocks.