Ayurveda explains this through the concept of daily dosha cycles: vata, pitta ,and kapha are each at their peak during certain times of the day. Ayurveda divides the 24-hour day into the of following time periods (they are approximate because they depend on the season and geographic location): The Daily Lifestyle Regimens are based on this concept.
Early in the morning, the sky is bewitchingly beautiful and all of nature is beginning to fill up with fresh energy. By afternoon, energy levels peak and appetite is sharp. In the evening we head home from work, while the birds fly back to their nests. Then comes the night, with its balm of restful sleep. These natural rhythms echo the qualities of the three doshas—one restless, another intesnse, and the third calm. In accordance with these rhythms, Ayurvedic philosophy divides the twenty-four hour day into distinct doshas zones.
Vata Time: 2:00 to 6:00 AM and 2:00 to 6:00 PM. The early hours of the morning and evening are ideal for active and creative work. This is why Ayurvedic practioners recommend rising in “Vata Time”. If you sleep late, you will feel dull and groggy because you have stepped into the next zone, which is Kapha time.
Kapha Time: 6:00 to 10:00 AM and 6:00 to 10:00 PM. Both of these are periods when you activity levels are either slowly increasing or slowly winding down. Therefore, rising after 6:00 Am or not going to bed between 6:00 AM or not going to bed between 6:00 and 10:00 Pm can cause disturbance sleep.
Pitta Time: 10:00 AM to 2:00 PM and 10:00 PM to 2:00 AM. Fiery pitta governs the productive hours from midmorning to the middle of the day and again late in the night when the digestive system is busy processing and assimilating dinner.
One way you can use this information to tell whether your dosha imbalance according to the time of day. For example if you find it difficult to say awake in the morning without cups of coffee, if could be because you have been rising late-during the lethargic kapha time. Try waking up an hour earlier, and your morning will be filled with verve.