Regardless of talking about news sitemaps or the publication date under your articles' titles, you have to use one, globally recognized format. If you don't do, Google News might be unable to include your articles in its index.

The proper datestamp is documented in the following W3C Note: http://www.w3.org/TR/NOTE-datetime

That said, both the publication_date tags in your News sitemap and the publishing date below your articles' titles has to be in the YYYY-MM-DD format.

Examples:

• In news sitemaps:

<news:publication_date> 2006-08-14T03:30:00Z </news:publication_date>

     Please note the spaces, too, before and after the date and timestamp.
     ZULU (Z) is the preferred time zone, GMT, that is, even if you're not in this time zone.

• In an article:

<h2>Example title</h2>
 
<p>by John Doe @ 2006-08-14</p>

If you're not comfortable with the numeric month expression, you may use the month's name as well.