Hi Henrik,
today (perhaps) it happened again, at least something similar. So, I've got a fixed returning weekday alarm, that I prefer not to change if I need to be woken up at a different time, so I use an "extra" alarm. Today then, I first set that extra alarm to a different time. Then I cancelled the current returning alarm. And then I still changed the extra alarm to some 10 minutes ahead. The flow triggered at the first time that was set, not 10 minutes later. I just tried something analogous, and it happened again. So it seems that with cancelling one alarm after setting a new one, and then changing that one to a later time, the flow keeps the first time...
To double-check, I started the flow with an alarm to later, then cancelled it (before setting a new time), added a new alarm to over a minute, and then changed that alarm to a few minutes ahead. Funnily enough the flow didn't trigger ... neither at earlier time nor when the alarm actually went off...
I also noticed (not really part of the issue but kind of related, perhaps): if I have a fork with a delay, and I stop that fiber, then the alarm will remain, eventhough that delay is cancelled. So, I have a flow with a timer that uses delays to vibrate every so often. If I pause it, it stops the fibre with the delays. There's another flow catching alarms, that gets triggered by those delays, also after the fibre was stopped. So it's not like a real bug, but perhaps helps in this issue, or at least worth considering to add some "cleanup" into the delay block, if it get's stopped to cancel the alarm...?
Hope this helps, let me know if I should do some more tests apart from what I mentioned, or if I wasn't clear.