Other mistake: In the shower scene, Marion Crane's palm looks water wrinkled as if she's been in the shower for quite a long time even though she was only in for a few moments before Norman stabs her. Also, when Norman drags her out of the bathroom, Marion's legs are stiff and together and she has her toes pointed.
Other mistake: If the film begins on Friday, December 11th and continues to the following week, there should be more Christmas decorations, not just the ones seen on the store when Mr. Lowry walks by Marion's car.
Answer: No, it was a Sunday. However, December 11th fell on a Friday in 1959, the year before release.
LuMaria 1