One way:
<?php
$text = <<<EOD
-------Sep 01-------
http://sitesesdfp2.com/
http://sitesesdfp21.com/
http://sitesepsdf31223.com/
http://randomsdfurl.com
-------Sep 02-------
http://sitesep2.com/
http://sitesep21.com/
http://sitesep31223.com/
http://randomurl.com
-------Sep 03-------
http://sitesep3.com/
http://sitesep21123.com/
http://sitesep23123.com/
http://randomurl32.com
EOD;
$chunks = preg_split('#(^|[\r\n]+)-+[a-zA-Z]+ \d+-+[\r\n]+#', $text);
$links = array_pop($chunks);
echo "<pre>$links</pre>";