Message delivered time

We’re coding new XMPP clients which report to each other the time a message is read by the far party.

Would extending the element with urn:xmpp:time from XEP-0202 like below be valid?

from='northumberland@shakespeare.lit/westminster' id='richard2-4.1.247' to='kingrichard@royalty.england.lit/throne'> My lord, dispatch; read o'er these articles. from='kingrichard@royalty.england.lit/throne' id='bi29sg183b4v' to='northumberland@shakespeare.lit/westminster'>
<time xmlns='urn:xmpp:time'>
    <tzo>-06:00</tzo>
    <utc>2006-12-19T17:58:35Z</utc>
 </time>