This adds another sorting option for directory listings. Using this simple modification you can sort listings by date.
Just 2 files need to be modified: main.tpl and /admin/conf_options.php

in main.tpl,
Locate

After that, ADD

{if $sort eq 'D'} | <span class="sort">{l}Date{/l}</span>{else} | 
<a href="?s=D{if not $smarty.const.ENABLE_REWRITE}&amp;c={$category.ID}
{/if}{if $search}&amp;search={$search}{/if}{if $uid}&amp;uid={$uid}{/if}
{if !empty($p)}&amp;p={$p}{/if}">{l}Date{/mgУ6FS

in conf_options.php
FIND

'OPTIONS'  => array(
                 'P' => _L('PageRank')    ,
                 'H' => _L('Hits')        ,
                 'A' => _L('Alphabetical')
                 ),

REPLACE BY

'OPTIONS'  => array(
                 'D' => _L('Date')    ,
                 'P' => _L('PageRank')    ,
                 'H' => _L('Hits')        ,
                 'A' => _L('Alphabetical')
                 ),

You are done!