Variable definition? I don't need it...

ChatController.php

private function calculateDuration($startTime)
    {
        $currTime = time();
        $diff =  $currTime - $startTime;

        if ($diff >= 3600) {
            // hours
            $difference = $diff/3600;
            $difference = round($difference,0);
            if ($difference>1) { $extra="s"; }
            $difference = $difference." hour".$extra."";
        }
        elseif ($diff < 3600) {
            // hours
            $difference = $diff/60;
            $difference = round($difference,0);
            if ($difference>1) { $extra="s"; }
            $difference = $difference." min".$extra."";
        }

        $duration = $difference;
        return $duration;
    }