It's difficult to be precise when dating photos, but I would estimate this to have been taken around 1867-68 at the earliest: the women's hoops are not the larger elliptical shape popular for several years before then. This is also around the time when hats worn on top of the head essentially took over the headwear scene from bonnets, and you can see that the two women in darker clothes are wearing these hats.

It's harder to give a potential end date. These are well-dressed women, so we can assume that their outfits bear a relation to what was currently fashionable, but they may not have been at the height of fashion for one reason or another: they might have been without access to a dressmaker who could make European styles for some time, they might be somewhat conservative, etc. It's unlikely that this was taken much after about 1872, by which time the bustle shape was quite pronounced and the sleeve tended to have a big cuff or ruffle or simply flare out at the end. Their skirts are also quite plain, and by 1869 having an overskirt or at least piles of ruffles was de rigueur.