One caveat: if you're not happy with your carving or are looking to improve, take it one decoy at a time. Otherwise, if you carve 12 decoys, you'll make the same mistakes on all 12, and have 12 decoys you aren't really happy with. In my opinion, its best to finish a decoy, look at where you can improve, then make another. When I started carving I didn't take it one at a time, but wish I did. I don't know your experience level, so I don't mean to offend if this advice doesn't apply.
If your goal is simply to have a hand carved rig by duck season, throw that advice out the window.