Boaty I guess commercialisation, that was day when you got time and a half on Saturday and double time on Sunday. I used to have to do it because our heat treatment furnaces ran24 /7 and parts needed to be inspected after treatment, cutting them up and polishing sample and viewing under microscope
It was all to do with the 5 day working week. When I worked in a shoe shop back in the 60s we closed at 1 o'clock on Wednesdays and each member of staff was given a morning off when you didn't have to come in till 1 p.m. Never on a Saturday, though, as that was the busiest day.