The topic has been brought up before & I’ll describe our use case:
We need a notification event triggered when a downtime is created.
When a downtime is created an email notification should be sent out to recipients responsible for systems not monitored by our Icinga instance to take care of the downtime on their side. These downtimes by default get scheduled at least several hours before the downtime starting.
Maybe someone has written an event listener / handler for this.