hanks, but it's not working. I discovered a /usr/share/gnome-background-properties/zorin-os-17-wallpapers.xml file that I need to edit in order to add new wallpapers. It's quite frustrating.
Interestingly, there's already a zorin-mountain-timed.xml file in Z16 that changes with the hours. It's a pity that it was altered from Z16 to Z17.