The XSLT Standart Library can be found at http://xsltsl.sourceforge.net/. I recently used version 1.2.1 for an airport flight information data system to format dates and times flights were arriving. The code was simple to use and well documented. It is distributed as a zip file and in order to use it you just need to include a directory with the library in it. In order to keep it simple I named the directory with the version.
To include the functions you would like in your xsl file you need to include an import function. The statements below show an import from the xsltsl-1.2.1 folder which was at the same level as the xsl. The date-time.xsl includes the functions.
<xsl:import href="xsltsl-1.2.1/date-time.xsl"/>
To call the format-date-time function you would add code like this to the xsl. The @actual is the field from your xml data that you are going to format.
<xsl:call-template name="dt:format-date-time">
<xsl:with-param name="xsd-date-time" select="@actual"/>
<xsl:with-param name="format" select="'%i:%M %Q'"/>
</xsl:call-template>