Display a post for a specific time !

Hello all
i want to display one post from a category for a specific time
e.g. for 1 week or 1 month

on search i found this useful code

<?php
// initialize new query of one post from category 11
$my_query = new WP_Query('cat=11&showposts=1');

// loop through the database to find related information
while ($my_query->have_posts()) : $my_query->the_post();

// set expiration time of two days
$goAwayDate = time() - (60 * 60 * 24 * 2);

// get date of sticky post
$postDate = get_the_time('U');

// if post is too old, do nothing
if ($postDate < $goAwayDate) {

// else show the post
} else { ?>

	<h1><?php the_title(); ?></h1>
	<?php the_excerpt(); ?>

<?php } endwhile; ?>

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I want to select 2-3 posts from a certain category
& then set show & expire time for each post i.e. 1 week or 1 month
& then using if else statement show the post as per the time period
& for else part (if all expired period expired) use the latest from that selected category 🙂

thanx in advance