Change the way dates are presented in WordPress's admin view

WordPress does not respect an admin's preferred date format.

Here's how the admin list of posts looks to me:

I don't want it to look like that. I want it in RFC3339 format.

I know what you're thinking, just change the default date display - but that only seems to work in some areas of WordPress. It doesn't change the column-date format. Here's what mine is set to:

So that doesn't work.

Instead, you need to use the slightly obscure post_date_column_time filter

Add this to your theme's functions.php:

 PHP//  Admin view - change date format
function rfc3339_post_date_time( $time, $post ) {
    //  Modify the default time format
    $rfc3339_time = date( "Y-m-d H:i", strtotime( $post->post_date ) );
    return $rfc3339_time;
}
add_filter( "post_date_column_time", "rfc3339_post_date_time", 10, 2 );

And, hey presto, your date column will look like this:

Obviously, you can change that code to whichever date format you prefer.