wp-admin/includes folder and look for the file
class-wp-posts-list-table.php, then go to the line 634, you will see this:
$h_time = sprintf( __( '%s ago' ), human_time_diff( $time ) );
change this line to:
$h_time = sprintf( __( '%s' ), gmdate('Y/m/d g:i:s A', $time) );
This will display as this:
2014/03/11 8:08:54 PM Published
in the Date column.
Now, I’m not sure how to overwrite this without hacking WP core.
Hope that helps,