When browsing the UI, next to the events, it shows only how many days ago the event got raised but not when exactly it was opened.
In the example below, it shows 8 days.
Aria Operation For Networks 6.x
vRealize Network Insight 6.x
To view the exact timestamp of an event, hover over the displayed relative time (e.g., "8 days ago") with the mouse pointer. The precise timestamp will then be shown in a tooltip.