DouKaku?

<?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/2005/xpath-functions"
  xmlns:my="uri:ja.doukaku.org:my-functions"
  exclude-result-prefixes="my"
  >

  <xsl:output method="text" />

  <xsl:template match="/" >
    <xsl:value-of select="my:DateEx('2008-09-01T10:02:38', 10000)"/>
  </xsl:template>


  <xsl:function name="my:DateEx" as="xs:string">
    <xsl:param name="dstr" as="xs:string" />
    <xsl:param name="sec" as="xs:integer" />

    <xsl:sequence select="xs:string(
      xs:dateTime($dstr) +
      xs:dayTimeDuration(fn:concat('PT',xs:string($sec),'S'))
      )" />
  </xsl:function>

</xsl:stylesheet>