It is and probably always will be general policy for Nexon to extend their usual maintenance by a number of hours with no explanation. They make bucketloads of money, and not enough of their customers complain. When they do explain themselves, they barely apologise, and everyone goes on like normal. Furthermore, they do not require maintenance to ban people, tweaking their user data does not need game servers to be downed for several hours.
Simply put, if you are going to hack. Don't be stupid enough to be caught.