If you purchase the AppleCare Protection Plan at the same time as your Mac, iPhone, iPod, Apple TV, or Apple display from the online Apple Store, Apple will register the AppleCare Protection Plan for you. If you purchase your AppleCare Protection Plan and your covered product separately or elsewhere, you will need to register your AppleCare Protection Plan.
Your AppleCare Protection Plan coverage starts from your hardware purchase date. Registering your AppleCare Protection Plan at a later date does not extend your coverage. In fact, there are many benefits to registering your AppleCare Protection Plan as soon as you purchase it.