That's exactly what I do. The weight of the water makes so little difference that is doesn't matter much as long as you stay within reasonable amounts. An entire gram of water will increase the density from 1.69 to 1.71 in a single puck of mine (3 inch diameter and I use 67 grams of powder or so). If you have that much water in there I thinks its too much. I personally only use only 2 sprays per pound. You just need to mix it in well. And to your point, it makes sense that time will also spread the moisture, but passing the mix through a 20 mesh screen works good enough for me.
I used that method a lot today and its gets me close to the desired target, I will get variations between 1.59 and 1.7 most in the middle. Once mixed in, the densities will average out. The more precise you are with the mark, the smaller that range will be. I need to pay attention because that compression occurs slowly over time so you can pass the mark easily. The more even your density is the more evenly your grains will burn.
Another point to note is that it may take some trial and error to get you right at the right range, not much, a few pucks will do. Theoretically I needed 74 grams, in reality I needed 67. Once you have that number though, its repetition.
Make sure that powder is spread out evenly in the die and that the ram is dead on center, you will be more accurate.
On a final note, have you ever measured the thickness of a puck before and after its dry?