public function estimatedDeliveryDateModifierForProduct($product, $qtyInCart) {

    //Is the product a pre order product?
    if ($preOrderDate = $product->getPreOrderDate())
    {
        $diff = date_diff(
            new DateTime,
            new DateTime($preOrderDate)
        );

        return $diff->format('%a');
    }

    //If it has to be backordered...
    if ($product->getQty() < $qtyInCart) {
        if (empty($product->getSupplierId())) {
            return Mage::getStoreConfig('supplier/stock_file/delivery_modifier');
        } else {
            return Mage::getModel('supplier/supplier')->getCalDeliveryTime($product->getSupplierId());
        }
    }

    if (Mage::Helper('catalog')->productIsBike($product)) {
        return 2;
    }

    //If we got here, the item is in stock and it
    //is not a bike. We can ship it in 1 day.
    return 1;
}