For those of you that use the built in Notifier app:
The following is my app for notifying me when the Garage Door has been opened for longer than 20 minutes.
However, it seems to be firing just as soon as the Garage Door is opened.
Am I setting it up correctly?
That looks fine to me, it seems to be exactly the same as when I have that at least the last time it ran was working normally. I think. I'm out walking the dogs, but I guess I'll have to test mine when I get home.
Could it have been a notification from a previous opening of the garage door? This would depend on what is considered the event with regards to stopping the notification, the contact sensor opening or after the 20 minute wait.
Just tested my Notifier automation on my garage door (and covers other doors, which were untouched during the test) and the automation worked as expected. Didn't get a notification until 20m after garage door opened. So I can't replicate.
FWIW I tested a second time w/same settings as you in notification app (in case it was related to the repeat which mine didn't have) and also could not replicate w/repeat added.
Check the "Events" page for your notification device (e.g., your phone) to see what app sent the notification command if you're not sure. Look for entries with "command" in the "Type" column that will likely appear right before the notification event itself.
App logging would be another way to help figure this out.
I wasn't able to prove my theory, it seemed to work for me as well. I think logging will be a help as @bertabcd1234 suggested. The only other thing to look at is whether the multiple contact sensors is having some impact, either in the way the app works, or even just in how circumstances play out when moving through the Garage.