How to Change the Critical Dates Format

By default, the dates are entered in a YYYY-MM-DD format (where YYYY is the year, MM is the number of the month, and DD is the number of the day. You can change the format (for example, to something like January 1, 2020) using an XSLT extension.

To add this functionality, use an Oxygen Publishing Template and follow these steps:

If you have not already created a Publishing Template, you need to create one. For details, see How to Create a Publishing Template.
Link the folder associated with the publishing template to your current project in the Project Explorer view.
Using the Project Explorer view, create an xslt folder inside the project root folder.

In the newly created folder, create an XSL file (for example, named merged2mergedExtension.xsl) with the following content:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  exclude-result-prefixes="xs"
  version="3.0">

  <xsl:template match="
      *[contains(@class, 'topic/created')]/@date |
      *[contains(@class, 'topic/revised')]/@modified">
    <xsl:attribute name="{name()}">
      <xsl:value-of select="format-date(., '[MNn] [D01], [Y0001]')"/>
    </xsl:attribute>
  </xsl:template>
  
</xsl:stylesheet>

Open the template descriptor file associated with your publishing template (the .opt file) and set the XSLT stylesheet created in the previous step with the com.oxygenxml.pdf.css.xsl.merged2merged XSLT extension point:

<publishing-template>
  ...
  <pdf>
    ...        
    <xslt>
      <extension
        id="com.oxygenxml.pdf.css.xsl.merged2merged"
        file="xslt/merged2mergedExtension.xsl"/>
    </xslt>

Edit the DITA Map PDF - based on HTML5 & CSS transformation scenario.
In the Templates tab, click the Choose Custom Publishing Template link and select your template.
Click OK to save the changes and run the transformation scenario.