Wordpress - get posts by date range

Im trying to get a list of posts from WordPress for the last 7,30 and 365 days.

Here is the code im using:

$args = array(
        'posts_per_page'=>10,
        'post_status'=>'publish',
        'post_type'=>'post'
    );
    if(isset($_GET['group'])){
        switch($_GET['group']){
            case 'week':
                $time = date('Y-m-d h:i:s',strtotime('-1 week'));
                break;
            case 'month':
                $time = date('Y-m-d h:i:s',strtotime('-1 month'));
                break;
            case 'year':
                $time = date('Y-m-d h:i:s', strtotime('-1 year'));
                break;
            default:
                $time = '';
                break;
        }
        if($time!=''){
            $args['pub_date'] = '>= "'.$time.'"';
        }
    }

    $query = new WP_Query( $args );

If I error_log the args array I can see the timestamp being set. But when I error_log the WP_Query object I can see the SQL query:

SQL_CALC_FOUND_ROWS  wp_posts.* FROM wp_posts  INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id) WHERE 1=1  AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish') GROUP BY wp_posts.ID ORDER BY wp_postmeta.meta_value desc LIMIT 0, 10

This query does not hold the pub_date date range I have set. How can I achieve this?

Credit goes to MichaelH in this Thread on wp.org forums. You could modify it, to fit your requirements.

<?php
  function filter_where($where = '') {
    //posts in the last 30 days
    //$where .= " AND post_date > '" . date('Y-m-d', strtotime('-30 days')) . "'";
    //posts  30 to 60 days old
    //$where .= " AND post_date >= '" . date('Y-m-d', strtotime('-60 days')) . "'" . " AND post_date <= '" . date('Y-m-d', strtotime('-30 days')) . "'";
    //posts for March 1 to March 15, 2009
    $where .= " AND post_date >= '2009-03-01' AND post_date <= '2009-03-15'";
    return $where;
  }
add_filter('posts_where', 'filter_where');
query_posts($query_string);
?>