I know that some radishes ('French Breakfast') are primarily early-spring-radishes ("Sow seeds in spring after last frost"). Some (or all?) daikons seem to be plant-in-summer for fall or winter harvest if you want roots instead of seeds.
But there are varieties that are earlier or later.
Kitazawa has 15 kinds of "giant white radish" and 11 white ones in the "Korean Radish" section.
http://www.kitazawaseed.com/se...
Minowase Summer Cross, Hybrid - for summer or fall harvest
http://www.kitazawaseed.com/se...
Mino Early - for summer to fall harvest
http://www.kitazawaseed.com/se...
April Cross, Hybrid - for late spring to early summer harvest and early winter harvest.
http://www.kitazawaseed.com/se...
Tokinashi, All Season - all-season daikon
Iwai Daikon - small - Sow seeds in late summer/early fall in a sunny location.
http://www.kitazawaseed.com/se...
Shirahime Hatsuka Daikon - small white radishes ... can be harvested as early as 20 days after planting. If temperature extremes are avoided, it is hardy enough to grow year-round.
http://www.kitazawaseed.com/se...
==