background-changer
This code programatically changes the desktop backgrounds to user-defined images. This only works on Gnome-based operating systems. I couldn't find a program that did this so I made my own.
Setup
Start by cloning the repo and opening background_changer.py. Change the background_images variable to the path of the folder containing images you'd like to cycle through. Also note that I set the dbus address in the constructor and I don't think this changes between distros, but I'm not positive.
Then open cron in Terminal with crontab -e and set the times when you'd like this code to cycle through backgrounds. You can either set your Python interpreter here or simply shebang background_changer.py. For example, I change my background everyday at midnight with this command: 0 0 * * * /usr/bin/python3.10 /home/kyle/repos/background-changer/background_changer.py. If you get any errors you can also capture the error by appending > /home/kyle/.cron_stdout_background.txt 2>&1 to that command.
As long as the required number of images are in the directory you set you should be all set!