I have planted brassicas right around, or slightly after, Labor Day a few times. If you don't get rain on them right away, then it will likely be a puny plot..or even a bust. However, if you get some good rain on them soon after planting then you can get a fair to good stand. So while it is late, it can still work...but you have to get rain and your turnips will not likely get very big. Also, don't skimp on the N, you will need it more than normal.
Radishes can get decent sized bulbs and in my mind deer prefer radish tops to turnip tops and you can definitely still get the above ground tops to grow fair. I would go with more radishes than normal if you are this late. FWIW, for a variety of reasons, I did not get my brassicas in until last weekend, but I was pleased to see very good germination this weekend. Now a few more good rains and I should have a pretty decent crop I think.