How to Make The Order Delivery Date A Required Field?

[trickobrien]

I have the order delivery date contribution installed,it works fine but some customers are checking out without specifying a date,I would like to make it a required field during checkout-how would i do this?

thanks in advance

[igofresh]

Just did it.
includes/modules/pages/checkout_shipping/header_php.php

edit as follows (black is existing and red is to be added)

//BEGIN Order Delivery Date
    if (zen_not_null($_POST['order_delivery_date'])) {
      $_SESSION['order_delivery_date'] = zen_db_prepare_input($_POST['order_delivery_date']);
    }
    $order_delivery_date = $_SESSION['order_delivery_date'];


if (trim($order_delivery_date) == '') {
    $messageStack->add_session('checkout_shipping', 'Please select a delivery day from 

the calendar', 'error');
    zen_redirect(zen_href_link(FILENAME_CHECKOUT_SHIPPING, '', 'SSL'));
}