Hi hippophile1,
If you use the "Schedule" function, you have the option to choose how long a listing will retry for if it fails to post immediately.
If you use the "Post" button and it doesn't post immediately, it will retry for 5 minutes.
If the listing status is "Retrying" or "Posting" then you shouldn't repost. If the status if failed, you're set to repost.
I hope this clears things up=)
-Mike