Enjoy your Saturday!
Prior to 1928, the stock market was open on Saturdays, but not Sundays. The Sunday closings were out of religious respect, and the fact that in those days most Americans lived on farms, and had to give their horses a day of rest or they would die...
During 1928 & 1929, as the stock market was in its "bubble phase", many Saturdays were taken off to allow exchange staff to catch up on their paperwork. For months after the stock market crash of late 1929, Saturdays were taken off to allow exchange staff to catch up on their paperwork...this time led by selling pressures. In the early 1930's, Saturdays began to be given off more often due to light trading volume, another result of the Crash and Great Depression.
From the 4th of July 1945 through Labor Day Sep 1945, the stock market was closed all Saturdays...since Victory in Europe was May 8th, 1945, and Victory in Japan was Aug 14, 1945, this probably also had the celebratory impact of wanting to close that summer starting with Independence Day.
Then, for many summers after that into the 1950's, the stock market was closed all Saturdays from Memorial Day through Labor Day. This begins to blend in the concept of, in general, society just wanting a shorter work week.
In the 1950's, the stock market began closing every Saturday...continuing this societal desire.