<?php
$text = '<p>2006-12-12</p> <p>2006-12-13</p> <p>2006-12-14</p> <p>2006-12-15</p>';
$date = preg_split("/[\s,]+/", $text);
print_r($date);
?>
<?php
$text = '<p>2006-12-12</p><p>2006-12-13</p> <p>2006-12-14</p> <p>2006-12-15</p>';
preg_match_all('~<p>(.*?)</p>~is', $text, $result);
var_dump($result);
?>