Prahar of a raag

Since I learned of the thing called prahar associated with each raag, I have been curious as to how this works. I googled it and came up with this page: http://ayurveda-foryou.com/music/raga_time.html, and http://www.ragopedia.com/raga/playtime.html . I learned that the 24 hour day is divided into 8 periods which are 3 hours each. Moreover, each time period has a mood associated with it, which is created by certain combinations of swars. I think that logically, shuddha swars should be sung starting at noon, and then gradually add komal and teevra swars as the time goes on. However, the raags are put together in a different logical order. It seems that there has been extensive study in the field of musicology as to what raag creates most emotion at what time. As a generalization, raags with the vadi in the poorvanga, are played in the evening, and the ones with the vadi in the uttaranga are played in the morning. So I was close, but not exactly right.