$showpasstime = '';
//將字串轉為時間 成功的話就表示格式正確
$chkd = DateTime::createFromFormat('Y-m-d H:i:s', $timedata);
if (isset($timedata) && $chkd === false) {
	$showpasstime = '';
}else{
	if($chkd->format('Y') > 1900){
    //轉回文字
		$showpasstime = $chkd->format('Y-m-d H:i:s');
	}
}

//時間戳->日期
date('Y-m-d H:i:s', $timestamp);
//日期->時間戳
strtotime("now");
//日期->時間戳
$dtime = DateTime::createFromFormat("Y-m-d", "2000-01-01");
$timestamp = $dtime->getTimestamp();
//調整時間
$dtime->modify('+6 month');
$timestamp = $dtime->getTimestamp();
//轉換格式
$date = "13-06-2015 23:45:52";
    echo DateTime::createFromFormat('d-m-Y H:i:s', $date)->format('Y-m-d h:i:s');