An internal service we relied on when working at Norway's biggest government agency had opening hours. If you called it outside 8-17 it wouldn't reply, heh.
I’m not saying no one should create a highly available web service. I am saying that this is one of those things that techies assume, and shouldn’t, because it’s a huge plus to hiring, business and engineering simplification, and morale if you can define away non-business-hour problems.