Kirby has a built in feature to include dates in your contents.
You could always add a simple field to your content files and write a date their just like this:
Title: Super Nice Content
----
SomeDate: 15/12/2011
----
…and afterwards in your template you could just parse that date with PHP and generate whatever you need:
<?php
$somedate = strtotime($page->somedate());
echo date('Y-m-d', $somedate);
// 2011-12-15
?>
But there's a nicer way to do that!
Whenever you need a date for your content, just add a date field to your content file:
Title: Super Nice Content
----
Date: 15/12/2011
----
Make sure the format you use for your date is parsable by php. Anything like dd/mm/YYYY
or YYYY-mm-dd
or many other formats will do. Read more about it here.
Date
is a predefined keyword, so Kirby will automatically take care of parsing the content of that field as a date and give you nice shortcuts to handle it in your templates.
<?php echo $page->date('Y-m-d') ?>
This will do the same as the example above – just in one line. As an argument you can pass any valid php date format string. If you don't pass any string the function will return a unix timestamp, which you can use to make some more fancy php date calculation stuff.
So if we take a look at our blog article template, it is very easy to include a date there and this is just a very general example.
<article>
<h1><?php echo html($article->title()) ?></h1>
<?php echo kirbytext($article->text()) ?>
<time datetime="<?php echo $page->date('c') ?>" pubdate="pubdate"><?php echo $page->date('d.m.Y H:i') ?></time>
</article>
It's up to you to customize that and build your own perfect article template.