Date Comparison Issue – Please Help

I’m troubleshooting an issue in a plugin. Basically the code never recognizes when a post is current as opposed to when it it future. It always assumes it’s a future post, which is wrong 99% of the time.

Here’s the code:
# Grab post date info
$post_year = $_POST['aa'];
$post_month = $_POST['mm'];
$post_day = $_POST['jj'];
$post_hour = $_POST['hh'];
$post_minute = $_POST['mn'];

# Add leading zeros to month
if ($post_month == "1") { $post_month = "01"; }
if ($post_month == "2") { $post_month = "02"; }
if ($post_month == "3") { $post_month = "03"; }
if ($post_month == "4") { $post_month = "04"; }
if ($post_month == "5") { $post_month = "05"; }
if ($post_month == "6") { $post_month = "06"; }
if ($post_month == "7") { $post_month = "07"; }
if ($post_month == "8") { $post_month = "08"; }
if ($post_month == "9") { $post_month = "09"; }

# Date diff calculation
$post_date = "$post_year$post_month$post_day$post_hour$post_minute";
$curr_date = date("YmdHi");
$date_diff = $curr_date - $post_date;

# If post is future dated
if ($date_diff < 0){

For some reason $date_diff is always less than 0. I know that the $post_date value is correct because later in the code, it gets printed into a table and I see it’s correct. That leaves me to suspect either that the $curr_date is incorrect or the subtraction of two date values as integers is going awry.

Anyone who has a better understanding of php and the inner workings of WP have an idea as to what’s happening?

Thanks in advance!