That isn't something I'd want to happen, it sounds like it creates a potential queue of scripts that will flood the system on start, if it works the way you described.
I prefer the deterministic behavior of cron, the script will run when it is specified to run, as you said earlier, as long as the system is running; and as I stated in a separate comment, it will run @reboot if I need it to run then.
> With @hourly I lose this control and multiple machines could potentially trigger backups at the same time
Then don't use @hourly, use staggered times, it's very easy.
This isn't what happens. If you leave it offline for days it'll only trigger the service only a single time.
100 jobs all running at different times throughout the week is a very different load than them all falling back and running at the same time on system boot.
There are two options to fix it;
Disable persist so no catching up on missing scripts. Set OnBoot=5m so it gets ran 5 minutes after boot, so your script (say backup) is ran on boot first, then every time on schedule
Enable persist but just add sleep in ExecStartPre - very "cron" way but there is just no in-systemd option to enable "catch up" script to be delayed
Sadly no option to "run catch-up timers with delay" at least yet
> Then don't use @hourly, use staggered times, it's very easy.
Not in cron. In systemd it's just RandomizedOffsetSec=30m and it is "stable" - same host with same job will always have same delay so on multiple hosts it is spread nicely. There is also non-stable version