Assuming we're talking about oak tan leather, which is correct to the period; a little neetfoot goes a long way. It can also make leather greasy, and let it stretch, maybe more than you want. I've found saddle soap to be real good at darkening leather without giving it a greasy feel, or getting it baggy.
My process usually is this: finish the article, saddle soap, especially the edges. Let it dry and evaluate the the color. Dye if necessary. Burnish the edges, then add neetsfoot sparingly.
You can dye thru saddle soap, but any oil, tallow, beeswax, etc makes it almost impossible to dye.
One other thing: use pure neetsfoot, not neetsfoot compound.
Hope this helps,
Moose