In your $args array, "meta_key" should be "event_time". If you want to get events after a certain date you also have to set meta_value to the desired date and meta_compare to >, <, etc..
Note however that you’re not going to be able to order the posts with the format "June 6 2012 6:00 PM", this isn’t a format that MySQL understands. You should be using the native datetime format yyyy-mm-dd hh:mm:ss.