How to get the Hours Difference (in HH:MM format) in PHP

It’s very simple to get the difference in hours using PHP

function timeDiff($firstTime,$lastTime) {
    $firstTime=strtotime($firstTime);
    $lastTime=strtotime($lastTime);
    $timeDiff=$lastTime-$firstTime;
    return $timeDiff;
}

echo (timeDiff("10:00","12:00")/60)/60;