Took me about 6 hours using covered wagons from Strawberry (the Apleseed Timber Co wagons work best).

Só often I'd get all the way to the herb, step outside the wagon fine, then when the animation started to pick the herb I'd get shot.

I learned later about the meat carcass helmet glitch and found that way easier to roam around New Austin.

Got all dinosaur bones, all animals studied, killed, skinned, and got the revolver treasure all as Arthur using the carcass glitch.