In Traditional Chinese Medicine, the chi/energy cycles through the body systems every 24 hours. Each organ is ‘center stage’ or at its peak for two hour periods.
Here is a list of the organs and their time frame:

LUNGS:   3:00 to 5:00 AM
LARGE INTESTINE:   5:00 to 7:00 AM
STOMACH:   7:00 to 9:00 AM
SPLEEN:   9:00 to 11:00 AM
HEART:   11:00 to 1:00 PM
SMALL INTESTINE:   1:00 to 3:00 PM
BLADDER:   3:00 to 5:00 PM
KIDNEYS:   5:00 to 7:00 PM
PERICARDIUM:   7:00 to 9:00 PM
TRIPLE WARMER:   9:00 to 11:00 PM
GALLBLADDER:   11:00 to 1:00 AM
LIVER:   1:00 to 3:00 AM