From Organic Design wiki

This template is not actually used, the #when parser-function is used to add time information to articles. Just add a single parameter which can be arbitrarily formatted time information, for example:

{{#when:2009/4/24}} - best to do dates backwards like this otherwise it tries to use some weird American format
{{#when:24 apr 2009}}
{{#when:24 apr, 4:30pm}} - current year is used here since not specified

The function expands to a set of category links to categorise the article into year, month, day-of-month, full-weekday-name and time (24 hour HH:MM:SS format). Articles exhibiting time can then be matched with a DPL query, for example:


The parser function which adds this is very simple consisting of the following when.php code in the LocalSettings.php file.