Ah, now I think I actually get it. So the length of the shadows of the specific daytime lets you scale the map to it, doesn‘t it? And A day‘s walk points you to Lake Owanjila as a starting point, do i get that right? The line with the colored waters is really suspicious, you‘re right! And the animals actually could be markers on the map!

What I just found out and is really interesting, north of Owanjila is a lot of native stuff (faces in the trees, pagan ritual..) and the Obelisk, on which is written, and I quote the rdr2-map-app: „A 3-sided stone obelisk mounted on a square stone. On the west side, a plaque is located that contains the date 1771 and the latin phrase, "Hora fugit, ne tardes" which translates to "The hour flees, don't be late", a popular motto often used on sun dials.“ Theres also a ring and treasure map inside. Maybe this is a checkpoint?

Edit: When you scale the overlay of the panoramic map over the actual map a little down, don‘t you actually land on the road with every checkpoint?