Windows update active hours constraint

I’m trying to avoid my machine rebooting while I am not around to exercise a modicum of control.

In my Windows Update settings I have disabled “get the latest updates as soon as they’re available” and I have “pause updates” set to 1 week.

In the advanced settings I have disabled “get me up to date”, and I have enabled “Notify me when a restart is required”.

Today I sat down to my PC to discover that it had terminated all my running programs and rebooted. Without any kind of prompt or warning. Which brings me to “Active Hours”.

Active hours can be set automatically or manually and I thought I could set them to 00:00 to 23:59 to prevent updates running without me being around. But no, Microsoft absolutely prevents the active hours from covering a period longer than 18 hours. Why???

So far as I can tell, I have done everything available in the settings to prevent what nevertheless happened at some point in the last 24 hours. I am not aware of an urgent zero-day security problem that demanded an instant patch. Why did my machine do a forced restart when so far as I can tell I have clearly insisted that it not do so?

I must be missing something! Any suggestions?