Just an observation from the 1960s and 1970s - this Saturday Morning book study idea was completely unheard of. It was tuesday night or nothing.
Believe it or not, some of the elders (my dad was one of them) who had lakeside vacation properties lobbied and got passed the amendment to move the service meeting/school to Thursday so that they could leave for the lake on Friday. Not popular with the CO, but it got done anyway.
Also, way back in the early sixties, it seemed that almost every cong in Oklahoma City had the Public Talk and WT Study on Sunday evening rather than in the morning. As I recall, the reason was given that we needed to be out in service on Sunday mornings, and also that having "church" on Sunday morning was just too much like christendom. This got moved to Sunday mornings pretty much on a district basis when a new DO came to town and suggested that more people would be home if we bothered them on Sunday afternoon instead.
Of course, in those days the circuit assembly was always 3 days, and I guess that got changed too.