All these studies are highly limited. In addition to general self-reporting issues, you can't say anything about natural day and night cycles unless you careful

All these studies are highly limited. In addition to general self-reporting issues, you can't say anything about natural day and night cycles unless you carefully control all light exposure (and ofc other stimulants like caffeine, exercise or simply noise) for an extended time. Noone available as participant in these studies would have been living like humans used to before artificial light. You can't expect an undisturbed circadian rythm from them.