Google the name of the variety of turnip you want to grow. You'll find information on the days to maturity. Without knowing what you're going to grow we can't give you much help.

I know this is late but have you tried Seven Top turnip greens? The plant does not produce a root like a turnip, just the greens and fully mature in 45 days. You can cut earlier for young, tender greens. I have grown these several years and many of my customers love them. I use them myself. They are great greens, easy to grow and you can cut-and-come-again with them.

turnips purple tops will grow all winter and produce early spring or sooner i plant them in the fall with ground cover green manure crop with collards kale chard mustard cabbages have harvest all winter there better after frost or freeze.