Duration between incident communication task plans

[bekfro]

I'm looking for advice on the best way to calculate the time between communication plans for our Major Incidents.  The ask is to report on the time between the tasks.  For example initial sends out at 8 am and the update needs to be sent at or before four from the initial, if a second communication needs to be sent that would be within four hours as well:

It would be the duration between created as the plans don't appear to close.  Should it be a metric, SLA, or maybe just a field on the table?  

[Abhay Kumar1]

@bekfroyou can create a field if you just need for reporting, Sla if yu want to trigger any other operation like notification, metric definition is as well with having flexibility to create report as per requirement but it will also create a new record in system.