But is often wrong itself.

Before 9's became a thing, people built systems that required outages, and those outages would happen outside of business hours.

However that's also why some transactions had to complete the next business day after they were registered. Because the whole business was running on offline processing (aka batch processing) that could be interrupted for upgrades, but had to be completed by the start of business the following morning.

My dad did one of those jobs, and my brain has made a bigger deal out of the times I awoke in the middle of the night to find him on the phone at the kitchen table at 2 am dealing with a war room call because an upgrade broke things that needed to be done in 5 hours. It probably only happened 3 times that I know about, and I probably knew about at least half of them, but it felt like it happened twice a year.