/* module: single_post_split.php */
  <?php
  $content = apply_filters('the_content', $post->post_content);
  $save = explode("</p>", $content);
  $count = 0;
  $arrsize = count($save);

  foreach ($save as $a) {
    if ($count == 3 &&   strcmp( date("Y-m-d", strtotime("-7 day")), get_the_time("Y-m-d") ) > 0  ) {
      echo "<div style=\"margin-left:2px; margin-top:-2px;\">";
  ?>

      <!-- AD BLOCK -->

      <!-- END AD BLOCK -->

     <?php echo "</div>";
    }

    $count = $count + 1;

    echo $a. (($count == $arrsize) ? "" : "</p>");
  }
  ?>