Set a simple countdown timer using custom fields

I’ve found a great little bit of PHP that will calculate and display how many days there are left until a certain date in the future.

<?
  $day   = 11    ; // Day of the countdown
  $month = 3;      // Month of the countdown
  $year  = 2011;   // Year of the countdown
  $hour  = 23;     // Hour of the day (east coast time)

  $calculation = ((mktime ($hour,0,0,$month,$day,$year) - time(void))/3600);
  $hours = (int)$calculation;
  $days  = (int)($hours/24);
?>

<p> <?=$days?> days</span> left to go</p>

Thank you, Joe Crawford http://lab.artlung.com/countdown/

My problem is I want to be able to specify the date that is being counted down to using Custom Fields specific to a particular post.

So I’ll have 3 custom field Names called “countdown-date”, “countdown-month” and “countdown-year” and get them to spit out the values in the PHP above.

So far my miserable PHP skills have come up with stuff like:

<?
  $day   = <?php get_post_meta($post->ID, 'countdown-date', true); ?>    ; // Day of the countdown
  $month = 3;      // Month of the countdown
  $year  = 2011;   // Year of the countdown
  $hour  = 23;     // Hour of the day (east coast time)
...

But these give me error messages. I hope someone would know how to do this.

This is within the loop.