The app measures the time each issue has been on a specific Status. The app measures even the previous duration the issue has been on a specific status. For instance, if initially the issue has been for 1 minute in TODO, then you move it to DOING, then you move it again to TODO. After a minute, it will report as 2 minutes spent in TODO status. After the installations the add-on can be accessed from the configuration page. You will see a link to jump to configuration right after installation. The calculated time is measured in days.