McFarlane seems to have stayed with the same simple arrangement of text on the back of his cdvs for the entire period, the only clue as to sequence, apart from fashion, being the card thickness. This first cdv, with the delicately hand tinted hair, earrings and buckle, is on thin card, 0.018" thick, and probably from the first year or two. Note that McFarlane retains the earlier job description of 'Photographist'.
When you have a successful format, why change it? The second cdv above is on card 0.020" thick and thus probably later than the one at the top, and the similar third above, 0.026", perhaps later again.
This cdv helpfully dated to 1867 is on yet thicker card (0.030") is thus probably later than those above, constraining the earlier two to a five year period.
This design on the reverse was used by a number of Glasgow photographers in the mid to late 1860s. (See McNab, Robertson, for example.) Its use here presumably dates to the period 1867 - 1870.