sort by date picker

i have this code :

<?php $catPost = get_posts(array('category'=>get_cat_ID( '' ),'numberposts'=>1));?>
<?php foreach ($catPost as $post) : setup_postdata($post); ?>

that take the last post i added.
i want it to take the post with the lastest date in the costum field

how can i do that?

http://wordpress.org/plugins/advanced-custom-fields/