Not precisely though since in different places, the sun goes up/under at different times.

An interesting thing could be if the small hands had a color that indicates the night/day/dusk/dawn

If you want a single-view visualisation of sunrise/sunset across the globe, there's always this design: https://www.timeanddate.com/worldclock/sunearth.html

I've always found it quite weird (though obviously convenient) that Warsaw and Madrid are on the same time zone

They are not. It is 17:25 in Warsaw now, 16:25 in Dublin.

Oops, not sure what city I was thinking of when I wrote Dublin

My point is that CET feels rather wide to me, so I guess substitute for Sevilla or Madrid

Right? A 'good enough' solution / update to the regular clock, I felt! :)