I have been practicing a biphasic sleep pattern for two months and it works well for me because I'm a student as well as a writer and doing this allows me to be refreshed while I study and while I write. But my pattern is a bit different from the suggested. I sleep for two hours from 4-6 in the evening and four hours from 3-7in the mornings. This seems to be more down time than most but compared to nine or so hours I would usually need to wake well rested it works out great for me. I'm not sure if this has any negative implications. I didnt exactly delve into research before I started but this sees to be a good rhythm for me. Why is it that the recommended pattern is 90 minutes then 4.5 hours?