Hi Slimboyfat,
P6 of the Photodrama of creation:
"The Darwinian theory has disappointed those who swallowed it without a sufficiency of demonstration as to its truth. - (1 Timothy 6:20) Recent demonstrations show that every mixture of species and kind, even where partly successful means a reversion to the original standards within the third or fourth generation in plants, flowers, fruits and in animals. The correct thought would seem to be that under Divine supervision various orders of creation were brought to a state of development and a fixity of species, not to be turned aside nor thereafter altered."
Russell seems to be saying the evolution occurred up until a specific point in time and then stopped. As you pointed out he viewed mankind as a separate creation.
By 1927 J F Rutherford specifically states that the whole creation (excluding the stars and planets) only took 49 thousand years (this period refers to the "preparation" of earth) - Reference the Book called Creation 1927. Rutherford seems to give latitude to the idea that some animal evolution could have happened. He keeps to Russell's idea that human kind was a separate creation.
Here's where the problem comes in. Because of the 49 000 year limitation and because evolutionary timelines were becoming more clearly defined showing that much longer periods were involved, it seems as if the Watchtower organization had to abandon the position totally.
So between 1927 (Creation book) and 1967 (Did Man Get Here by Evolution or by Creation?) it seems as if evolution was discarded. I would say it probably also happened after Rutherford died in 1942.
I hope somebody else can narrow it down further.