Earlier quoted context omitted.
Well I think they refer to the genetic make-up of the circadian timing system, as mentioned in https://en.wikipedia.org/wiki/Night_owl .
Most modern night owls just have very bright whole-house lighting and a world-class 24/7 carnival in their pockets.
Also, I have started thinking about my Night Owliness, as a manifestation of avoidant character in general. The "waiting till deadline to do a sprint" type of mentality.