As a side note I want to mention that I use Night Shift on mac os and every day!!! I need to switch it back on because there is no option to leave it enabled all day long.
It sounds like you’re trying to schedule Dark Mode to stay on all the time, which can be accomplished by choosing “Dark” in System Settings-> Appearance in Ventura or later, or in System Preferences-> General in Monterey or earlier.
https://support.apple.com/en-ca/guide/mac-help/mchlp1109/mac