wp changing dates

<?php
// define mysql connect
$dbname = "dbname";
$dbuser = "dbuser";
$dbpass = "dbpass";
$dbhost = "localhost"; // this can usually stay 'localhost'

$wp_table = "wp_posts"; // define wordpress table name

$gmt_offset = '-8'; // -8 for California, -5 New York, +8 Hong Kong, etc.

$min_days_old = 1; // the minimum number of days old
$max_days_old = 20; // the maximum number of days old

// connect to db
mysql_connect($dbhost,$dbuser,$dbpass);
mysql_select_db($dbname);


$result = mysql_query("SELECT ID FROM $wp_table WHERE post_type = 'post'") or die(mysql_error());
while ($l = mysql_fetch_array($result)) {
    $post_id = $l['ID'];
    echo "Updating: $post_id <br>";

    $day = rand($min_days_old, $max_days_old);
    $hour = rand(0, 23);

    $new_date = date( 'Y-m-d H:i:s', strtotime("-$day day -$hour hour") );
    $gmt_new_date = date( 'Y-m-d H:i:s', strtotime("-$day day -$hour hour -$gmt_offset hour") );

    mysql_query("UPDATE $wp_table SET post_date='$new_date', post_date_gmt='$gmt_new_date',
    post_modified='$new_date', post_modified_gmt='$gmt_new_date' WHERE ID='$post_id'")
    or die(mysql_error());

}

echo "<hr>DONE!";

?>