I have successfully changed the date format to US format on the front end using the 2.5 language override, but I can't figure out how to change it in the Admin section in the items table in the Created and Modified columns. These still show up in this format: 23/08/2012 - 23:40. Ideally, I would like the month/date/year format. Please help.

Any ideas on how to change this date format? Here is the screenshot of what i am talking about.

I know this is an old thread, but for anyone else...

This is done via the language override in the administrator/language/overrides directory. As of now, there doesn't seem to be a way in Joomla! 3.x to set the 'location' to 'administrator' via the back end language override function. It seems to be hardcoded to 'site'.

So just manually create a language file (e.g. 'en-GB.override.ini') in administrator/language/\overrides with the desired override. In this case:

worked for me.