Courtroom scenes show Georgia flag incorporating Confederate battle flag. Movie takes place in 1947; this flag wasn't adopted until 1956.
The wall clock in the execution room is an electronic digital clock because the second hand jumps to advance one second at a time. A wind up clock from that era would not have a second hand. An electric clock would show a second hand that moves at a constant steady angular velocity.
During the courtroom scene, Sheriff Potts (Cash) is wearing a contemporary wristwatch with an expansion band.