'Return the datetime value to use as Order Date (``date_order``) for the
Purchase Order created to satisfy the given procurement.'

def _get_purchase_order_date(self, schedule_date):

    self.ensure_one()
    seller_delay = int(self.product_id._select_seller(quantity=self.product_qty, uom_id=self.product_uom).delay)
    return (schedule_date - relativedelta(days=seller_delay))
