Menghitung selisi waktu

<?php

class TestController extends Controller
{
    public function actionIndex()
    {
        $time1 = '11:30';
        $time2 = '12:00';
        list($hours, $minutes) = explode(':', $time1);
        $startTimestamp = mktime($hours, $minutes);

        list($hours, $minutes) = explode(':', $time2);
        $endTimestamp = mktime($hours, $minutes);

        $seconds = $endTimestamp - $startTimestamp;
        $minutes = ($seconds / 60) % 60;
        $hours = round($seconds / (60 * 60));

        echo "Time passed: <b>$hours</b> hours and <b>$minutes</b> minutes";
    }

    public function actionReal()
    {
        if(isset($_POST['Apaaja']))
        {
            //Collect semua data dari form
            $model->attributes = $_POST['Apaaja'];

            //Ambil data waktu_awal dan waktu_akhir
            $time1 = $model->waktu_awal;
            $time2 = $model->waktu_akhir;

            //Prosesnya disini . . . . . .
            list($hours, $minutes) = explode(':', $time1);
            $startTimestamp = mktime($hours, $minutes);

            list($hours, $minutes) = explode(':', $time2);
            $endTimestamp = mktime($hours, $minutes);

            $seconds = $endTimestamp - $startTimestamp;
            $minutes = ($seconds / 60) % 60;
            $hours = round($seconds / (60 * 60));

            //Siapin data hasil proses yg akan masuk ke database
            $model->selisi_jam = $hours;
            $model->selisi_menit = $minutes;

            if($model->save()){
                $this->redirect('index');
            }
        }
    }
}