carbon setCourseTime cant pluse all video time

i have one course and this course have any episodes. i can recived one by one episodes time and save in database but i cant save plus episodes time in course time. i recived episodes time with this code

 protected function getCourseTime($times)
        {
            $timestamp = Carbon::parse('00:00:00');
            foreach ($times as $t) {
                $time = strlen($t) == 5 ? strtotime('00:' . $t) : strtotime($t);
                $timestamp->addSecond($time);
            }
            return $timestamp->format('H:i:s');
        }

i use this method for pluse all time episodes

public function setCourseTime($episode)
{
    $course = $episode->course;
    $course->time = $this->getCourseTime($course->episodes->pluck('time'));
    $course->save();
}

and my store controller is

 $episode = Episode::create($request->all());
        $this->setCourseTime($episode);

via Chebli Mohamed