Hey,
I had a quick look at this extension and have some suggestions:
* Escape ALL variables in HTML you are building. You can use
htmlspecialchars, the methods of MediaWikis HTML class, and in this case
probably want to just construct the whole thing with XmlSelect.
* You are not fully following the style guidelines. The spacing is off and
you are using underscores in var names instead of lowerCamelCase. See
http://www.mediawiki.org/wiki/Manual:Coding_conventions
* Don't use the 'description' in wgExtensionCredits, use
'descriptionmsg'
instead, and properly internationalize it.
Next to that it looks great, although I'm not completely sure the i18n is
all in order when using the native PHP time functions :)
Cheers
--
Jeroen De Dauw
http://www.bn2vs.com
Don't panic. Don't be evil.
--