iTunes works entirely from the feed, which lists the episodes and the media files. If the files are preset on the server but not referenced in the feed iTunes will not know they are there.
However you can only do what you want by uploading amended versions of the feed at intervals. If the files are referenced in the feed they will show in iTunes, if not, not. You would need a way of automating uploads of the feed; you can't do it within iTunes.
The timed release is a feature we offer on libsyn.com
You upload your episodes - create the post for each one - then you can pick the day and time in the future you want each post to go live.
Set it up once then you are all done.
Let me know if you need more details on this.