How should I configure my OS so that theme of stackoverflow changes according to time of the day?

I’m using Ubuntu 18.04 and I want stackoverflow’s theme to be change according to time of day: light theme when daytime and dark theme when night. In the site settings, when I set theme to "System setting" it sometimes sets Dark theme and sometimes Light. So I guess it respects my OS’s configuration but I’m not happy with the intervals. I want it to change to Dark theme after 19.00 for example. Is this possible?