It only took about 30 seconds for Nellie to remove the bullet from Boswell. An experienced doctor like Doc Adams could never (and probably never has) remove a bullet that quickly.
Dudley: "Well, that was yesterday Miss Susan. Today I wouldn't have you on a whiskey bet."
Matt: (to Nellie) "You know, if I'm ever down this way with a bullet in me, I'm gonna have them bring me to you."
Susan: "You know something Marshall? It seems to me that trash like that, men that rob banks and take advantage of innocent people, get more attention tham decent hard working citizens."
In the beginning of this episode, we see a grave marker with the dates 1824 - 1869. Later in the episode, we are told that the person buried there has been dead for 8 years. This tells us that this episode takes place in the year 1877.