They had better provide flexibility for all the complexity and tedium they introduce. It takes creating two new config files of about 10 lines each and a long system command to set up the simplest possible systemd timer.
I was pretty shocked that I needed to have three files. My backup script, a systemd service to call the backup script, and a systemd timer to call my systemd service that calls my backup script.
It took A LOT of fiddling and reading the Arch wiki before I had everything working as I wanted it to.
You can also find more documentation on the official systemd website, or Gentoo, CoreOS, and RedHat's website.
As an example: https://wiki.gentoo.org/wiki/Systemd#Timer_services
1) create systemd service to call your script
2) create a systemd timer to call that service