Systemd timer units are usually two: one for the service you want to run, one for the timer file.

I think you're confusing systemd timer units with Cronie[0], a crond implementation that I think predates systemd? It's possible there's some systemd thing I don't know about though!

I think most distros at least have an installable crond

[0]: https://github.com/cronie-crond/cronie/

Cron is still part of posix standard