Install an application called Variety. That allows you to change the wallpaper at specific intervals. So if you want the Night wallpaper to run from 1900 to 0700, you can do that.
Of course, depending on where you are in the world, the length of nights and days may vary during the year.
Hard Way
I'll sketch out how this works, if you're interested.
GNOME has a dynamic wallpaper by default, and it's using only an .xml file to swap the photos. I suggest you just look at how it looks and write your own, it's not that hard. And you can have much more than 2 images.
There's an easy way, and a hard way.
Easy Way
Install an application called Variety. That allows you to change the wallpaper at specific intervals. So if you want the Night wallpaper to run from 1900 to 0700, you can do that.
Of course, depending on where you are in the world, the length of nights and days may vary during the year.
Hard Way
I'll sketch out how this works, if you're interested.
GNOME has a dynamic wallpaper by default, and it's using only an .xml file to swap the photos. I suggest you just look at how it looks and write your own, it's not that hard. And you can have much more than 2 images.
https://www.linuxjournal.com/content/create-custom-transitioning-background-your-gnome-228-desktop