$re = '/^Deadline[:\h]+
(?|
(?=(?:\[(\d{4})-(\d{2})-(\d{2}))) |
(?=[A-Za-z]+,\h+.*?(\d{4})) (?=.*?,\h+(\w+)) (?=.*?(\d{2}))
)
/xm';
$str = 'Deadline Saturday, August 02, 2014 6:17 AM
Deadline: [2014-08-27 16:00:00 [Central European Time]]
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php