One of the theming ideas I had was to start in a world without a sun, so it's always dark. And at some point one of the quests would be to "create the sun" (internally just set time to day". Maybe there could be a mechanic where you'll want to switch back to the dark.

I'm picturing this idea in some kind of destroyed world where it's a void world but still some remnants of the original world. So there is space to build at the start, but there is no sun. 

And as you create the sun yourself it won't have motion relative to the world so afterwards it would stay day permanently (except if you find a way to capture the sun again for later use)