Congrats, it looks fantastic, it is obvious you have worked hard on the details, (deceptively) simple graphics notwithstanding.
There are multiple kinds of clouds, which can spawn at specific heights. They are spawned at semi-random intervals.
The stars only shine after midnight, they are dull at dusk.
Every object's colour values are separately changed according to the time of day. There is a delay between UI and scene dawn/dusk times because you're supposed to be far away and looking at the distant city.
I can write all day about this stuff, as I'm very excited but I'll control myself for now :)