Why try to re-invent the wheel?
Systsemd-timers aint hard to use…
You just need to read the man pages to learn the “new way” 
Plus it will automatically have the “don’t run again when already running” functionality build-in…
Eg: systemd Timers start a service, which is not started again when that service is already running
Nice read for all of you: Restart plasmashell on a schedule: Cron? Systemd timer? Edit system file? - #17 by TriMoon as an answer to the post just above it. 
@rethus sorry i don’t answer image only issues…