get_post_time of a specific post

<?php
//display date for post id 502
$one=get_post(intval(502));
if ($one) {
echo mysql2date("F j, Y", $one->post_date);
}
?>

Hmm, I’m not sure that code will get me to where I need to go although I could be interpreting it incorrectly. Let me give some context. I’m trying to put together a list of posts on the single post page that match a specific custom field value. Then I want to take that list and attach an icon indicating that it’s a new post. I’ll attach the important parts of code I’m using.

<?php
	global $wpdb;

	$findposts = $wpdb->get_results(
		"SELECT *
		FROM $wpdb->posts
		LEFT JOIN $wpdb->postmeta ON ($wpdb->posts.ID = $wpdb->postmeta.post_id)
		WHERE $wpdb->postmeta.meta_key = 'Serial'
		AND $wpdb->postmeta.meta_value = '$serial_value'
		AND $wpdb->posts.post_status = 'publish'
		AND $wpdb->posts.post_type = 'post'
		AND $wpdb->postmeta.post_id != $id
		ORDER BY $wpdb->posts.post_date ASC"
	);
?>

	<ul>

<?php $limit = 6; ?>
<?php foreach ($findposts as $findpost): ?>
	<?php $counter_serp++; ?>
	<?php $fp_id = $findpost->ID;
		$fp_title = $findpost->post_title;
		$fp_url = $findpost->guid;
                $fp_date = $findpost->post_date;
	?>
	<?php $mylimit=60 * 86400; $post_age = date('U') - $fp_date;?>

		<li class="related">
			<?php if ($post_age <= $mylimit) { ?><span class="info_icon new">New</span> <?php } ?>
			<a href="<?php echo $fp_url; ?>" title="Permalink to <?php echo $fp_title; ?>"><?php echo $fp_title; ?></a>
		</li>

	<?php if($counter_serp >= $limit) break; ?>
<?php endforeach; ?>
	</ul>

So basically I need to either get the post date by post ID and convert that to seconds so I can compare or convert the post_date string into seconds. Any ideas? Thanks.

Nevermind, I think I got it. Using the bit of code you showed before, I changed it to output the date in Unix format. Thanks for the help.