Open Device edit page.
Scroll down to the “Notification Options” section and select from the created Notification Groups
The Alert Escalation option allows you to “Start Alerts after Downtime remains for longer then:” a specific period of time. In the example above, the First Group is notified in 10 min, the Second Group after 20-minutes of downtime, and the Third Group after 30-minutes of downtime. The Notification Escalation time intervals in the drop-down menu range from immediate to three hours and are available in 10-minute increments.