In itself, the publication date is not significant. An exact date is only important for a relative handful of bestselling authors. For readers, it increasingly matters little, with all books becoming variously available for sale at different times in different parts of the world through online databases and retail. But the month is helpful to have something to hook the marketing systems around. We generally gear any publicity we do around the month of publication and the few months following rather than a specific day. The book will be available for sale when it arrives at the warehouse.