The 12 Main-Organ currents are the primary distributors of Qi. The complete sequence of flow happens over the course of a 24 hour period. Beginning at 3 AM the lungs fill with Qi. By 5 AM the lungs have reached their highest volume and the emphasis proceeds to the Yang paired organ to the lung: the large intestine. At 9 AM the stomach begins receiving it's fill. The diagram shows the full sequence.
This sequence underlies several important principles of Traditional Oriental Medicine. Have you ever noticed that many Tai Chi classes meet at 4 AM? Especilly in China they do. The Qi is at it's greatest volume in the lungs at that time. Breakfast is the most important meal of the day because most people eat it during the stomach time of 7 AM - 9 AM. As the Supreme Comander of the organs the heart receives all of the Qi of the emotions. By midday we've gotten most of the daily news that might affect us and we can use the refreshing new Qi in our hearts.