public function calcDurationBasedOnEndDateTime($end)
    {
        $startDate = strtotime($this->StartDateTime);
        $endDate = strtotime($end);

        $duration = $endDate - $startDate;
        $secsInDay = 60 * 60 * 24;
        if ($duration > $secsInDay) {
            //Duration cannot be more than 24h
            return false;
        }

        //info on this calculation here:
        //http://stackoverflow.com/questions/3856293/how-to-convert-seconds-to-time-format
        $formatDate = gmdate("H:i", $duration);

        return $formatDate;
    }