I’m not sure about changing the time duration of the siren, but you can certainly use “modes” to determine whether it will activate at all and which sensors will activated when.
The scheduler intro might help:
(March 2018: All of the following applies only to the SmartThings Classic app. If you purchased your hub after March 1, 2018 and are using the new “SmartThings (Samsung Connect)” app, creating rules works differently.)
You’ve got your hub. You’ve got some devices. Now how do you schedule what happens when?
SmartThings doesn’t have a rules engine/scheduler, so there’s no one tutorial for how to do this. But it’s an open platform, and there are about 12 different ways to set up various kinds of schedules. Some require custom code, some don’t.
A “scheduler” in this context is anything that causes a networked device to perform an action, even if it’s just to toggle on or off immediately. (Network engineering definition, forgive me.