If your looking to grow large radish and PTT roots then plant 90 days prior to your average first frost date and fertilize heavy. If you want tops then 45-60 days prior will give you Great tops.
Brassica will keep growing well past first frost dates unlike many other crops. If you have had a hard time getting the deer in your area to eat them I would plant later as opposed to sooner. I find myself planting later and later every year. I think the deer like them better when they are smaller anyway.
Edit: If planting via TNM/roll I would maybe plant a week earlier than If doing traditional tillage.
We plant ours mid to late July. I am prepping fields now to plant July 15-17 when I have a few days off, weather permitting. Deer hammer ours and I am looking for as much growth as possible. I have planted all through August with decent results. Labor day and after yields less than desirable results for us.