First of all, we all have a circadian clock than is run endogenously by differential gene expression and controls our change in awakeness, temperature, hormone levels, etc.. Circadian clocks are not exactly 24 h and they vary among people: some people have shorter clocks and other have longer ones. Apparently, people who have shorter circadian rhythms are morning people, and those that have longer one, are night owls.
How is this possible? In the following article "https://www.futurity.org/biological-clocks-sleep-disorders-protein-mutations-2289312-2/" it says that a 20-hour biological clock will make a person fall asleep earlier because they will get tired earlier and they will get awake also earlier. But for me, that would only be possible the first period or two if both cycles start at the same point time. Afterward, the cycles will get out of phase and that will not be true any longer.