The textual description of windowing query q18 (see 4.2.18) says "Calculate the time needed to process an order from the request up to the shipping.".

However, in the query "and" has a higher priority than "or". Hence, any ShipNotice element is sufficient to end the window. I suggest to force precedence in the query as follows:

declare variable $seq := fn:doc("cxml.xml");

<result>{
  for sliding window $w in $seq/sequence/* 
    start  $s when $s[self::OrderRequest]
    end  $e when $e/@orderID eq  $s/@orderID
   and
   (
     $e[self::ConfirmationRequest] and $e/@status eq "reject" 
     or
    $e[self::ShipNotice]
    )
  where $e[self::ShipNotice]
  return 
    <timeToShip orderID="{ $s/@orderID}">{xs:dateTime($e/@date) - xs:dateTime($s/@date) }</timeToShip> 
}</result>