WordPress文章显示过期提示

//display a message on older posts
function so_older_post_message () {
    $posted = get_the_time('U');
    $current = current_time('timestamp');
    //Convert difference in seconds to days
    $diffTime = ($current - $posted) / (60*60*24);
    if($diffTime > 365) {
        echo '<div class=older-post-message>' . __('This post was written more than a year ago and <em>might</em> not be entirely accurate anymore.', 'wptips') . '</div><br />';
    }
}
add_action('get_template_part_content','so_older_post_message');