Parmail-Parveshak Raags:
A ‘Parmail-Parveshak’ Raag contains qualities from more than one category discussed in the last post. If you keep performing the Raags on their given time, you will see that there is no sudden change in notes. The ‘Parmail –Parveshak’ Raags make the gradual change form one time slot to the other. For example, when it is time to go from Shudh ‘Re-Dha’ Raags to Komal ‘Ga-Ni’ Raags, Raag ‘Jai-Jai Vanti (name) fits right in there. It has Shudh ‘Re’ and ‘Dha’ and Komal ‘Ga’ is introduced along with the Shudh ‘Ga’. So gradually, the change is made from the second category to the third.
‘Poorvang-Vadi’ and ‘Utrang-Vadi’ Raags:
Once we are done with the basic theory, we shall discuss Poorvang and Utrang (upper and lower tetrachords) in detail. Here I am only discussing these in their capacity to affect a Raag’s time slot. This theory goes parallel with the above categorization. In this theory an octave is divided into two overlapping (only for determining the time of a Raag?) parts.
(If the keynote is ‘C’):
The first group is called ‘Poorvang’ (lower half)
The second group is called ‘Utrang’ (upper half)
We already know that the ‘Vadi’ note is the king note of any Raag. If a Raag’s Vadi note is from the lower half of the octave, that Raag is called a ‘Poorvang-Vadi’ Raag. If the Vadi Note is from the upper half of the octave, the Raag is called an ‘Utrang-Vadi’ Raag.
The Poorvang-Vadi Raags are performed from noon to midnight. And the Utrang-Vadi Raags are performed from midnight to noon. 
Once you know the Vadi note of a Raag, which is very important to know if you want to know a Raag, you already know which half of the day it goes to. It is also true that a Raag’s Vadi and Samvadi suwars reside in the opposite halves of an octave. So switching a Raag’s Vadi and Samvadi notes will in fact, change a Raag’s time by 12 hours. Normally, ‘Poorvang’ and ‘Utrang’ are not overlapped. That is a very widely accepted concept and makes a lot of sense when explaining the advance Thaat system. But here, when a Raag has ‘Pa’ Vadi and is considered a Poorvang-Vadi Raag, we run into problems. There is no other solution but to overlap Poorvang and Utrang. When divided this way, both parts share three notes (S, M, P). And whenever one of these notes is the Vadi note of the Raag in question, do not rely on ‘Poorvang-Utrang’ theory and check it otherwise. There are many Raags, which have a ‘Ma’ Vadi and are performed in the morning and with ‘Pa’ Vadi performed in the evening. So once again ‘Sa, Ma or Pa, if any one of these notes is Vadi, check the Raag for its ‘Komal’ (flats) and ‘Shudh’ (natural) notes, check the flow of the Raag. If Raag seems to stay in the upper half regardless of its Vadi note, then it is an ‘Utrang’ type (upper half) Raag and will fit into midnight to noon time slot or vice versa. The confusion has been created by continuous change in the popular style of Raags.
Wheel of Time:
As I mentioned earlier, the time theory divides a day into 8 pehars, morning and evening Raags overlapping two pehars. Here is an illustration showing how the day is divided. If needed, we will later see how the Raags fit on this wheel.
Conclusion:
Many new performers do not pay intention to the time theory at all. Their argument is that nowadays Raags are not always performed live. If the performer wants to record an evening Raag, and the only available studio time is in the morning, he has to do it. And who knows at what time a listener is going to hear the recorded material. An evening classical TV or radio show cannot limit itself to Raags only available in that time slot. So slowly, the time theory is fading out. However, it is good idea to learn about a Raag’s time slot because it adds so much to its personality.