Can't use any of the xdt functions! Grrrr

Hi,
I'm primarily using Saxon 8, but I've also tried this in XML Spy 2005,
and can't get it to work in either so i must be doing something wrong.

I originally started this by looking for how to convert milliseconds
into a date.  I came across....
http://www.xslt.com/html/xsl-list/2005-02/msg00499.html
where Michael Kay gives this formula:
xs:dateTime("1970-01-01T00:00:00") + $in * xs:dayTimeDuration("PT0.001S")

I assume, that "xs:dayTimeDuration" is typo or from an older version
of the spec and now should be "xsd:dayTimeDuration"?

Anyway, I've tried countless variations of the namespace (where do I
get the 'real' xdt namespace used by saxon??? I've just been
extracting them from various online examples) and cannot get
'dayTimeDuration' (or anything using xdt) to do anything for me.

---  here's one of the many iterations of stylesheet I've used ---------

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:fn="http://www.w3.org/2004/07/xpath-functions"
xmlns:xdt="http://www.w3.org/2004/07/xpath-datatypes"
xmlns:rs="http://java.sun.com/xml/ns/jdbc">
	<xsl:output method="html" omit-xml-declaration="yes"/>
	<xsl:template match="/">
		<xsl:value-of select=" (current-date() +
xdt:yearMonthDuration('P1Y')) +  xdt:dayTimeDuration('P1D')"/>
	</xsl:template>
</xsl:stylesheet>



---------------- Here's the stack trace-------------------

javax.xml.transform.TransformerException: No function found matching
xdt:yearMonthDuration with one argument
    at net.sf.saxon.TransformerHandlerImpl.endDocument(TransformerHandlerImpl.java:121)
    at org.apache.xerces.parsers.AbstractSAXParser.endDocument(Unknown Source)
    at org.apache.xerces.impl.XMLDocumentScannerImpl.endEntity(Unknown Source)
    at org.apache.xerces.impl.XMLEntityManager.endEntity(Unknown Source)
    at org.apache.xerces.impl.XMLEntityScanner.load(Unknown Source)
    at org.apache.xerces.impl.XMLEntityScanner.skipSpaces(Unknown Source)
    at org.apache.xerces.impl.XMLDocumentScannerImpl$TrailingMiscDispatcher.dispatch(Unknown
Source)
    at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown
Source)
    at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
    at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
    at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)



--------------------------------------------------------

Ideas??? Thanks!