I understand from previous threads that you can do this from the closed listing section within Auctiva and still get the re-list credit from Auctiva. I don't think you can schedule though, you just have to post it straight away.
I would suggest that you do some homework first and see if there are any improvements you can make to your listings before re-listing them. If you haven't already do a closed item search and compare your items against your competitor's.
Good Luck