$year1 = mt_rand(2000, 2020);
    $month1 = mt_rand(1, 12);
    $days1 = mt_rand(1, 31);
    $hours1 = mt_rand(1, 24);
    $minutes1 = mt_rand(1, 59);
    $seconds1 = mt_rand(1, 59);
    $date_1 = new DateTime("$year1-$month1-$days1 $hours1:$minutes1:$seconds1");
    echo $date_1->format('d.m.Y H:i:s') . '<br>';

    $year2 = mt_rand(2000, 2020);
    $month2 = mt_rand(1, 12);
    $days2 = mt_rand(1, 31);
    $hours2 = mt_rand(1, 24);
    $minutes2 = mt_rand(1, 59);
    $seconds2 = mt_rand(1, 59);
    $date_2 = new DateTime("$year2-$month2-$days2 $hours2:$minutes2:$seconds2");
    echo $date_2->format('d.m.Y H:i:s') . '<br>';

    $difference = $date_1->diff($date_2);
    echo $difference->format('d.m.Y H:i:s');