hide div Content after a certain time ?

i am building a News site. I want to display 1 featured post from “prime” category for only few hours. after it should be expired or disappeared from the section.

please have a look here u can see the post on top.

<div id="prime_news" class="col-full">
 <?php $the_query = new WP_Query('category_name=prime&showposts=1&orderby=post_date&order=desc');
    if ($the_query->have_posts()) :?>
<div id="prime_headline">
<?php while ($the_query->have_posts()) : $the_query->the_post(); ?>
<?php endwhile; ?>
<div class="prime_left fl">
<h3><a href="<?php the_permalink(); ?>" title="" class="title_slide"><?php the_title(); ?></a></h3>
<p class="prime_excerpt"><?php echo limit_words(get_the_excerpt(), '190'); ?><span  class="read-more"><a href="<?php the_permalink(); ?>"><?php _e('???  ???...', 'BharatNews'); ?></a></span></p></div>
<div class="prime_right fr"><?php bharti_get_image('image',560,320,' '.$GLOBALS['align']); ?></div>
</div><div class="clear"></div>
    <?php endif; ?>

 </div>