I don't think cytokines are "released" at any particular time of day. I try not to quibble with terminology so I know what you are saying. Cytokines are released during inflammation to signal the immune system to fight threats and repair injuries. Cytokines are small proteins that are produced by cells in response to pathogens or other stimuli. I don't think they are released because it is 4 a.m.

What seems more accurate to say is how IL-6 is "regulated." There is an increase in IL-6 levels from the evening, continuing during the night, followed by a drop in the morning. This pattern closely follows circulating cortisol levels which regulate inflammation. The whole process involves the HPA axis and the important function of cortisol to regulate inflammation in order to maintain homeostasis.