Just a few of the many things that affect our circadian rhythms (sources - American Sleep Association, Sleep Foundation, American Academy of Sleep Medicine, National Sleep Foundation, to name a few):

EXERCISE: when you do it, how often, what type of exercise, all have strong effects on our circadian rhythms (CRs, from now on)

FOOD INTAKE: when, how often, what kinds of foods (ie caffeine, alcohol, chocolate), all have strong effects on our CRs

STRESS LEVELS: affects hormones related to sleep like adenosine and melatonin; excess production of cortisol not only affects CRs but can affect relative amount of REM and stage 4 sleep (stage 3 or 4 depending on the source you use and when the research was conducted)

Other things that can alter CRs: Exposure or lack of exposure to light; exposure to digital screens and blue light; varying temperatures of your environment; how you choose to schedule your sleep

in fact, until about 200 years ago, people generally slept in 2 shifts - "first sleep", around 4 hours, generally around 10 to 2 AM or 9 to 1 AM, then got up, hung out, talked, partied, and went back to sleep from 3 to 7 or 2 to 6.

in other words, researchers have shown for many decades that circadian rhythms are not predetermined by genetics. Very little is, as we know from epigenetic research. it's appealing to think things like weight and CRs and depression, etc are determined, because when we are unable to change our habits our mind set it seems like a relief to have something to blame.

However, if we set aside "blame" altogether (as if the only choice is to blame ourselves or blame our genes) we discover there's a complex interplay between genetic influences, behavior, state of mind, and the awareness or quietude underlying all experience.

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All of the above is not to say I disagree with the author's main premise: We all need something between 6 1/2 to 7 1/2 hours of sleep (for the last 10 years, 7 hours on average has been found to be optimal; it is only a small minority that need more than 7 1/2 - but (almost) everyone needs more than 5.

if you find that getting up at 5 facilitates a healthy morning routine, get to bed by 10:30 at the latest. If you don't fall asleep right away, you'll need to adjust that, however.