Functions for XSLT conversion between dateTime format and Epoch format.

dateTime_to_epoch.xml

<xsl:call-template name="dateTimeToEpoch">
  <xsl:with-param name="dateTimeValue" select="$value"/>
</xsl:call-template>

<xsl:template name="dateTimeToEpoch">
  <xsl:param name="dateTimeValue"/>
  <xsl:value-of select="( dateTime($dateTimeValue) - xsd:dateTime('1970-01-01T00:00:00') ) div xsd:dayTimeDuration('PT1S')"/>
</xsl:template>
  
<xsl:template name="epochToDateTime">
  <xsl:param name="epochTime"/>
  <xsl:value-of select="xsd:dateTime('1970-01-01T00:00:00') + ($epochTime * xsd:dayTimeDuration('PT1S'))"/>
</xsl:template>