ExpirationDate option outputs in the XML the object expiration date-time (see http://forum.teradp.com/topic.asp?TOPIC_ID=448). For example, if the 'img' object with id 6494 expires on May 6th at 11:57 PM (UTC), executing ../do.ashx?cmd=objsnav&ids=6494&options=ExpirationDate produces:

  <img nav:objectType="img" nav:expirationDate="2011-06-05T23:57:53.833Z" id="obj6494" . . .>

    . . .

  </img>

If the object does not have an expiration date the attribute 'nav:expirationDate' won't be present.