This is not actually handled within Helpdesk.  You will need to go into NS to do this.  Go to the tasks tab, and expand the folders unti you find Incident Resolution > Incidents > Helpdesk > Notification Policies and create a policy there or clone an existing one.

As a reference point, you can clone and modify the policy titled Open Incidents with No Activity in N Minutes.  You will need to add an E-mail automated action to the policy, remove the report automated action, and set the schedule to run according to your needs.

You can add specific data from your query into the subject/body of your email.