How to get Ingress portal ownership duration?
Since June 2014 portal ownership date has been removed from Intel Map. You need to track manually the date you capture your portals.
Unfortunately this is currently not possible, or rather, you have to do it yourself.
Yes, this is possible by using the Ingress Intel Map - if you click on a portal there, you see the owner and the date since which they have held the portal:
If you use IITC it is displayed on the portal info screen on the right in the form of owned since date/time. If you hover over it, then it gives an actual owned time.