$re = '/\n*\d+:\d+:\d+\.\d+,\d+:\d+:\d+\.\d+\n(.*)/';
$str = '0:04:10.700,0:04:11.360
but
0:04:11.360,0:04:15.680
but it was plenty big you know the silo itself would have easily been
0:04:16.180,0:04:18.420
as wide as this room is
0:04:18.420,0:04:23.200
and perhaps larger and many, many, story\'s tall, you know because it was nested underground';
$subst = "$1 ";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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