If you asked this question of my wife, you will get an entirely different answer than from me.
She starts putting things in the spare room about two weeks in advance. I, on the other hand, tend to be a "last minute packer", because if I pack too far in advance, I find myself putting in a lot of clothes I end up not wearing.
We usually "cross pack" - half of our stuff goes in the other one's bag. We don't pay too much attention to the weight. You gotta have what you gotta have, right?
On the other hand, our carry ons weight about 50 pounds each......