Row daily. Your body recovers while you rest. Your body responds and becomes stronger based on how you stimulate it.
The medical community knows much about our daily rhythms. And they are studying it to understand it better.
Is it an internal clock? Or is it a response to the 24 hour cycle of daylight? It appears a little of both. No question something is going on - just exactly what and how is subject to study.
And is it a 24- hour thing or a long-term thing - consider that one cycle of the rhythm probably only makes sense in the context of a longer whole, a series - in this case, weeks and months.
You do not have to understand the 24-hour clock or bodily rhythm to use it to your advantage. You can do your own study.
Row, lift weights, cycle, run, swim, do something physical that gets you out of breath for an extended period of time. Then, over time, try missing some days and see how your body responds. Try rowing every day and compare how your body responds. Try rowing more easily or more firmly and see how your body responds.
Row a day for a year (with or without gaps to test the practice) and see how you feel. More on that coming. . .