suffix title with “EXPIRED” when scheduled post has reached it’s published date

I’ve found the code below that does what I want except it isn’t accurate to the hour. It is only accurate to the whole day, so if my post expires in the morning it still shows it as current in the afternoon.

How would this be able to be more accurate to the hour?

<?php if (strtotime($post->post_date) > strtotime('+1 minute')): ?>
<p>current</p>
 <?php elseif (strtotime($post->post_date) > strtotime('-999999999 days')) : ?>
<p>expired</>
<?php else : ?>
 <?php endif; ?>