Sort Directory Listings by Join Date

Could you please provide guidance on how I can get the directory listings to sort by join date?

I believe the necessary modification would need to be made in dr_listinglist.php as this is the file responsible for the category results page.

The following chunk of code appears to be what calls the category results:

<?php the_dr_categories_archive(); ?>
<div class="clear"></div>

<?php if ( have_posts() ) : ?>

<?php while ( have_posts() ) : the_post(); ?>

I need guidance on what to add to the above so that the category listings are sorted by the 'posted on...' date indicated in each individual listing.

Thanks so much!