====== 日付 ～DateTimeクラス～ ======
<code>
<?php
$date = DateTime::createFromFormat('j-M-Y', '15-Feb-2009');
echo $date->format('Y-m-d');
?>
</code>

======   ======
===== 今日  =====
<code>
$nowtime = new DateTime("now");
</code>

===== 昨日  =====
<code>
$yesterday = new DateTime("now");
$yesterday->sub(new DateInterval('P1D'));
</code>

===== 現在時刻  =====
<code>
$now = $nowtime->format('Y-m-d H:i:s');
</code>