See if this can get you started:
<xsl:template name="convertDate">
<xsl:param name="datestring" />
<xsl:param name="d" select="substring-before(substring-after($datestring, ' '), ' ')"/>
<xsl:param name="mmm" select="substring(substring-after(substring-after($datestring, ' '),' '), 1, 3)"/>
<xsl:param name="m" select="string-length(substring-before('JanFebMarAprMayJunJulAugSepOctNovDec', $mmm)) div 3 + 1"/>
<xsl:param name="y" select="substring(substring-after($datestring, $mmm), 3 , 4)"/>
<xsl:param name="ymmdd" select="10000*$y+100*$m+$d"/>
<xsl:param name="mm" select="substring($ymmdd, 5, 2)"/>
<xsl:param name="dd" select="substring($ymmdd, 7, 2)"/>
<xsl:value-of select="concat ($y, '-', $mm, '-', $dd, 'T')" />
</xsl:template>
Calling this template with a datestring parameter of "Fri, 15 Nov, 2013 @ 3:20pm" will return a value of "2013-11-15T". The time portion is left as an exercise for the reader.
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