Release : 12.2
Component : CA NetMaster Network Automation
The current design and architecture is about recurring alerts, as those are going to be alerts that will span across multiple monitoring intervals. Recurring alerts are those alerts that have potential to last hours and days and it would be nice to know exactly how long it took for the alert to be closed (and yes, by 'closed' it is referring to the last occurrence, not the actual close time).
A regular alert that hasn't recurred means it was a one shot deal, and at the next interval it was closed, so most likely the elapsed time will always be the monitoring interval.