Guidance Required: Notification Trigger Based on Cumulative New/Pending Duration Reaching 18 Hours

[vigneshr5]

In case staging table when changing the status to New or Pending and related metrics  duration should sum as 18 hrs  (before 24 hrs breach) and  send Notification on 18 hr . Can you please suggest How to achieve this? 

Note :

If the case enters the New or Pending state multiple times, the duration for each occurrence should be sum. Once the total duration reaches 18 hours, a notification should be triggered.

[vigneshr5]

 There will be other status as well which should not be considered. Only these two statuses should be considered for the duration calculation which is attached as a screenshot