This is a simple script that changes the Plasma Breeze theme according to a custom time or according to your location's sunrise/sunset using a systemd timer.

The default is setting the theme to dark at 9:30 p.m. and back to light at 6:30 a.m.

Installation

Use the installer.sh script to set up automatically

$ git clone https://gitlab.com/dataprolet/plasma-theme-switcher
$ cd plasma-theme-switcher
$ sh installer.sh

Optional:

Change the service file to specify which script to use.
Change either script to a custom time or custom location.

Install manually

Place the timer and service file in the user directory ~/.config/systemd/use
Place the script into a directory and specify the path in the service file
Change the time in the script if necessary (the default is 9:30 p.m. and 6:00 a.m.)
Alternatively use the theme-switcher-sun.sh script to change the theme according to your location's sunrise/sunset and specify a location in the script
Enable and start the timer:

$ systemctl --user enable theme-switcher.timer  
$ systemctl --user start theme-switcher.timer