There is virtually no standardization or commonality. Many ryu consider the ranks as levels of initiation which have no parallel to dan and kyu. Still others broke the ranks down simply as student and teacher, of possibly various levels. For now, this answer is restricted to kendo as adjudicated by the Canadian Kendo Federation. Iaido has different test requirements but the comments on experience and ability are still fair.
Different countries have differing examination requirements but they are roughly similar.
For ranks below ikkyu, the kata is dropped. I'm not sure of the time for nanadan and hachidan, but they still require an exam. Kudan is granted without examination. Aside from the number of kata changing, the exam is the same for all ranks. It takes less than half an hour.