What would be the process for BlackBerry App World to submit new release of existing application and make it available on a specific date? This is a 'free' application
You cannot specify an app to be released on a specific date, regardless of whether it's a new app or a new version of an existing app.
With new apps your app will be reviewed and approved by RIM but not posted for sale until you click the 'release for sale' button. For new versions of existing apps your updated app is placed for sale as soon as it's approved. You will receive email notification when this happens.
As a rough guide here's how long it takes for apps to reviewed and published: