Answer: Daikon raddishes may be harvested at any time. They, like other raddishes, will get a bit tough and more pungent if you let them grow for a long time after they reach full size. There are numerous varieties all of which reach somewhat different sizes, shapes, and sometimes even color. So experience with a particular type is useful. It is best to harvest them before they bolt (send up a seed head).
Try harvesting a few once they reach an acceptable size and continue to harvest weekly, noting any changes in quality. The days-to-harvest on the seed packet is also a good general guide to use.
Q&A Library Searching Tips