Sorry Jason I misunderstood your instructions.
As I understood it you set the session when you pressed the button on the Checkout page and then the Confirm page collected the data from the session and added to cart
I deleted the sessions from the Checkout page and added to the Confirm Page
I have tried again but it is still not working
I copied this field into the form section of the confirm page as well ( so there are 2 sessions on the page in blind fields both called NextDay )
<input name="NextDay" type="hidden" id="NextDay" value="<?php echo((isset($_POST["NextDay"]))?$_POST["NextDay"]:"") ?>" />
I attach Zip File as still not working