Displaying Recent Posts in the Last 12 hours only

Well after 2 hours of Googling, i’ve only found how to show recent posts in the last day. I actually haven’t even got that to work.

Does anyone have any idea on how I can accomplish showing posts made in the last 12 hours only?

If it’s not possible, then I’d settle for the last day only:
Here’s what I got for that, but it’s not working

<ul id="news">
<?php
$current_day = date('j');

$recent = new WP_Query("cat=1&showposts=100&day='.$current_day.'"); while($recent->have_posts()) : $recent->the_post();?>

<li>
<h2><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
</li>
<?php endwhile; ?>
		</ul>