Then you have never looked for it. This is pretty basic stuff taught in the very first year of the medical school.
>when stressed rushing to a doctor’s office visit
Even has a name: white coat hypertension.
>I suspect blood pressures varies wildly through the day, and this variation depends on a person’s physiology.
Yes it absolutely does. Just like your heart rate varies throughout the day, your BP keeps changing as well. That's why we like to measure it over 24 hours before any diagnosis.
To get you going here is a 2009 article on labile hypertension. It discuss the topic but does not provide any quantitative information on population distribution.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8673041/
Edit: here’s a link to a more recent reference:
https://www.imperial.ac.uk/news/251055/blood-pressure-variab...
Apparently, contrary to your assertion that an individual’s blood pressure variability is part of established 1st years med student’s knowledge, labile hypertension seems to be an active area of research.