Some scientists are awakening to the possibility that there are variations in sleepiness related to time of day. Other scientists are already awake to that possibility. All scientists are to some or other degree either likely or unlikely to read this study about the matter:
“Comment on Short-term Variation in Subjective Sleepiness,” C.A. Eriksen, T. Akerstedt, G. Kecklund and A. Akerstedt, Perceptual and Motor Skills, vol. 101, no. 3, December 2005, pp. 943-8. The authors, are at the Institute of Psychosocial Medicine and at the Karolinska Institutet in Stockholm, Sweden, explain that:
The authors explain: “It was concluded that there are large variations in sleepiness related to time of day.”