Where should I put this code??

Hi. I am trying to get wordpress to have set titles of each post based on Category – Day – Date. I edited the single.php file and it’s working!! The only problem is the title doesn’t show up as a “title” in the category view or when the front page is pulling a list of posts.

Where should I post this code to make it happen??

<?php
$today = get_the_date($d, $the_post->post_parent);
$day = date("l");
$categories = get_the_category($postID);

?>

<h1 class="content-title"><?php echo $categories[0]->cat_name ?> - <?php echo $day?> - <?php echo $today?></h1>

The website is:

http://truthfrequencyradio.com/network