I have set the Dark mode in OP8Pro to turn on automatically according to custom time range (6PM to 6AM), Unfortunately it does not do the work it suppose to. I only able to turn it on manually.
I have mine set from sunset to sunrise. Dark mode enabled, but when I restarted my device, it went back to light mode.
Not sure why and also unsure if it's related to the issue you're having but I thought I'd mention it. Didn't matter to me too much as I was just testing the scheduling. I normally use substratum themes so I don't typically have automated light/dark mode.