I used this plugin to duplicate a prior post and make edits. When I saved it as a draft, the plugin captured the time of the save as the post date. When I made the final edits a couple of days later and published the post, the post date did not reflect the publish time but rather the time I duplicated the post. If you use the wordpress 'guid' field for anything (like I do in a mysql query), that needs to be edited as well to point to the proper permalink. In the Manage Posts screen, the duplicated post (as a draft) showed a post time rather than the conventional WordPress indication of 'unpublished.'
If you duplicate a post, quickly edit it and publish it, it's fine.