Its the Last Activity date that the app checks for. The Generic zigbee outlet driver has a bug (I call it a bug anyway) where it only pushes an event if the state of the device changes. Really it should push the event no matter what and let the hub decide if its a change or not. If it pushed the event every time the Last Activity would update when you refresh the device and when it reported any events.
I did find out that if power reporting is turned on (even if device does not report power) then the Last Activity will update. I think I ran into some other odd side effect so I ended up turning it back off.
And yes reporting its status every 3 minutes is excessive. You could try resetting it and pairing it again, it will drop right into the same device on the hub so no harm in doing it. May fix whatever setting is bugged up and making it report so often.
Here is my favorite activity check app: [RELEASE] Device Activity Check - Get notifications for "inactive" devices
