my_template_fragment.xsl

<xsl:template name="short-time">
		<xsl:param name="date" /> <!-- YYYY-MM-DD HH:MM:SS +/-HHMM -->
		<xsl:variable name='hour' select='substring($date, 12, 2)' />
		<xsl:variable name='minute' select='substring($date, 15, 2)' />
		<xsl:variable name='second' select='substring($date, 18, 2)' />
		<xsl:choose>
		  <xsl:when test="contains($timeFormat,'H')">
		    <!-- 24hr format -->
		    <xsl:value-of select="concat($hour,':',$minute,':',$second)" />
		  </xsl:when>
		  <xsl:otherwise>
		    <!-- am/pm format -->
		    <xsl:choose>
		      <xsl:when test="number($hour) &gt; 12">
			<xsl:value-of select="number($hour) - 12" />
		      </xsl:when>
		      <xsl:when test="number($hour) = 0">
			<xsl:text>12</xsl:text>
		      </xsl:when>
		      <xsl:otherwise>
			<xsl:value-of select="$hour" />
		      </xsl:otherwise>
		    </xsl:choose>
		    <xsl:text>:</xsl:text>
		    <xsl:value-of select="$minute" />
				<xsl:text>:</xsl:text>
				<xsl:value-of select="$second" />
		    <xsl:choose>
		      <xsl:when test="number($hour) &gt;= 12">
			<xsl:text>p</xsl:text>
		      </xsl:when>
		      <xsl:otherwise>
			<xsl:text>a</xsl:text>
		      </xsl:otherwise>
		    </xsl:choose>
		  </xsl:otherwise>
		</xsl:choose>
	</xsl:template>

original_template_fragment.xsl

<xsl:template name="short-time">
		<xsl:param name="date" /> <!-- YYYY-MM-DD HH:MM:SS +/-HHMM -->
		<xsl:variable name='hour' select='substring($date, 12, 2)' />
		<xsl:variable name='minute' select='substring($date, 15, 2)' />
		<xsl:choose>
		  <xsl:when test="contains($timeFormat,'H')">
		    <!-- 24hr format -->
		    <xsl:value-of select="concat($hour,':',$minute)" />
		  </xsl:when>
		  <xsl:otherwise>
		    <!-- am/pm format -->
		    <xsl:choose>
		      <xsl:when test="number($hour) &gt; 12">
			<xsl:value-of select="number($hour) - 12" />
		      </xsl:when>
		      <xsl:when test="number($hour) = 0">
			<xsl:text>12</xsl:text>
		      </xsl:when>
		      <xsl:otherwise>
			<xsl:value-of select="$hour" />
		      </xsl:otherwise>
		    </xsl:choose>
		    <xsl:text>:</xsl:text>
		    <xsl:value-of select="$minute" />
		    <xsl:choose>
		      <xsl:when test="number($hour) &gt;= 12">
			<xsl:text>pm</xsl:text>
		      </xsl:when>
		      <xsl:otherwise>
			<xsl:text>am</xsl:text>
		      </xsl:otherwise>
		    </xsl:choose>
		  </xsl:otherwise>
		</xsl:choose>
	</xsl:template>