Unless I’m missing it, can’t use power allowance (default ST app) for less than 1 minute.
Have a siren that I’d like to auto off after 5-10 seconds. Ideas?
- can’t get MY brain around CORE yet -
SmartThings’ official features don’t schedule in less than a minute because to be honest you can’t guarantee that in a mesh system. Let alone a mesh system combined with a cloud platform. 
Core can definitely let you enter a shorter timeframe, which may work or may not. Or may work on one day and take longer on the next.
For industrial applications, you would use a siren that had the timer built into the Siren itself, rather than trying to do it with a networked command.
If you’re willing to use core, you can try it and see. It’s going to depend a lot on the specifics of your local network.
There are lots of people in the peer assistance thread who will be glad to help you.