Red Dead Redemption 2 Beard Tips

I tried to grow the longest beard possible in Red Dead Redemption 2. To do so, I locked Arthur Morgan in a hotel room in the town of Valentine, and I made him guzzle hair tonics and go to bed without dinner 59 days in a row. Consider this video a scientific report.
I did not shave for all of chapters one and two. By the beginning of chapter three, a tutorial popup told me I would have to use the "hair tonic" item to grow my beard longer than it had grown by that point. It said that each hair tonic is good for one unit of hair growth, though what does that mean? How many nights of sleep does it require for a tonic to have an effect on my hair growth?
To find the answer, I conducted a scientific experiment which consumed six hours of my real life and 59 days of Arthur Morgan's virtual one. Did this experiment result in my achieving a perfect "10" in all facial hair categories? No. Did I learn anything interesting in the process? Maybe. Did I narrate this video with the bizarre vocal affectation and word choice of a late 19th-century politician? Definitely.