There is just too many unknowns to predict when the deer might catch on to it. Brassicas look like Beet tops or Turnips kind of - and will stay green into winter quite a while. Because the plot is not large enough to keep to sustain any deer, they will only feed on it as they pass by, and only if their security is not compromised. It could be your getting as much feeding on it as your going to get.

If you have acorns in the area, or other mast, you should see a pickup on feeding on the patch-plot once it drops.