How To Insert the Current Date in the Cover Page
Oxygen PDF Chemistry provides a CSS extension, oxy_xpath, that can be used to execute XPath functions, including the fn:current-date function that simply returns the current date.
For example, if the text of the title is set in a 
  <booktitle> element, you can
      use a synthetic block with the date content like
      this:    booktitle:after {
        content:oxy_xpath("current-date()");
        color:gray;
        display:block;
    }