Here you go man, I made it in your Lumbermill, 2 steps:
Material Layer (Doodads0.blp) -> Filter Mode = 'Blend'
Geoset Animation manager -> Alpha -> Interpolation Type = 'Linear'
1 = zero transparency (the windows are lit); 0 = full transparency
So, 66667 frame is set to 1, then the material starts becoming fully transparent in 68667 when it is set to 0 and so on... You might know this, ofc.
Attached just in case
That is a truly canonic animation for the buildings in Blizzard style, hope you'll nail it
P.S. You should have black windows of the same size right behind this texture and I think you have ones.