Two years ago the deer mowed my turnip plot down to bare ground after they got up about 3" tall in mid September before the acorns started falling heavily, well before the first frost. I know that this goes against the conventional wisdom that brassicas in general, and turnip greens in particular, do not get utilized by deer until after a frost or two. I guess the deer around my place haven't read that chapter on deer behavior and feeding yet! I didn't get my fall plots in until a couple of weekends ago since I was trying to time my planting with some rain, but I noticed yesterday that the turnips, oats and arrowleaf clover were up and growing, and there were several deer in the plot that I can see from my house.
My plots with rape in them do tend to be utilized a little later than my turnip plots.