Formatting Actual Duration in a Custom Report

Change the field reference to use format-duration function.

<td class="Timespan">
  <xsl:call-template name="format-duration">
    <xsl:with-param name="t" select="ActualDuration" />
  </xsl:call-template>
</td>

Define the function as presented below.

<xsl:template name="format-duration">
  <xsl:param name="t"/>
  <xsl:if test="$t != ''">
    <xsl:variable name="ss" select="round($t * 3600)" />
    <xsl:variable name="h" select="floor($ss div 3600)" />
    <xsl:variable name="m" select="floor(($ss - $h * 3600) div 60)" />
    <xsl:variable name="s" select="$ss - $h * 3600 - $m * 60" />
    <xsl:value-of select="concat($h, ':' ,format-number($m,'00'), ':', format-number($s,'00'))" />
  </xsl:if>
</xsl:template>

Example of a template: