Hi @Daanm7
This is interesting!
I run quite a few schedule triggers myself, but i always like even numbers 
like 8h, 4h, 2h, 12h
I finally have a good reason to stick with this habit
With that in mind, here’s my guess as to what’s happening:
- What we likely expect: A rolling timer. “Run this workflow, wait 9 hours, run again.”
- What this trigger probably does: “Run this whenever the clock hour is divisible by 9.”
Since 24 is not divisible by 9, the execution hours are likely fixed at 00:00, 09:00, and 18:00.
(You might want to check your execution history to see if those are the only times it ran.)
I’m not 100% sure this is exactly how the cron logic works, so I’d suggest letting it run for a full day to observe when it actually triggers..
This is the file I based this guess on: