Not a definitive answer, but a couple of things that might help narrow it down.
That "Preparing for Restart / Managed by your IT Administrators" dialog looks like Apple's own enforcement prompt rather than the Automox one. My understanding is that macOS updates pushed through MDM get enforced by Apple's declarative management, and Apple draws its own notifications and picks its own deadline in that case. If that's what's happening here, it would explain why you're not seeing the Automox deferral buttons and why the 8pm deadline doesn't match your 6h x 2 config. Worth asking support directly whether the deferral settings actually apply to macOS OS updates or only to Automox initiated restarts, because the wording in the console isn't exactly clear on that.
On the sleep question, yes, I'd move the policy earlier in the day. A Mac lid closed at 5pm isn't going to do anything at 8pm, and then you get exactly what you're describing, it wakes up the next morning with a pending restart and goes off at the worst possible time. Mid morning or right after lunch has worked better for us, users at least see the prompt while they're at the desk.
I'd also check the agent version on the affected machines, the screenshot mentions the deadline logic only applies on 2.1.x and later. If you do open a ticket, grab the agent logs off the Mac first, that's the first thing they'll ask for.
