Get Posts updated or published within the last x hours

here is a shorter version that assumes the GET parameter ?time=[integer] (for example ?time=8)

add_filter('posts_where', 'filter_where', 11);
function filter_where($where="") {
    if(isset($_GET['time'])){
        $time = $_GET['time'];
        $time=(int)$time; // only allow integers
        if(in_array($time,array(8,24,72))){
            $where .= " AND post_date > '".date('Y-m-d H:i:s', strtotime('-".$time." hours'))."'";
        }
    }
    return $where;
}