The seeds tend to germinate in just a few days and can be full grown radishes in less than a month. There are summer and winter radishes, and these two crops should be switched during the year to keep radish production going yearround. The winter radishes tend to be larger and have to be in a deeper tub. Radishes can be pulled as needed, and then new radish seed can be replanted as space is available. Raidishes can go to seed if they get too hot, so you might need to provide partial shade during the hottest part of the summer.
Radishes can burst if they have been exposed to water and then rapid drying.
Since this is likely in a tub overpour system, it might be wise to put a funnel in the tub and pour water deeper than the developing roots. Also, radish leaves are usually very soft in hydroponic culture and suitable for use in soups and salads. If planted among greens, such as turnips or mustards, radishes will serve to deter insects from invading the greens. The majority of radishes are grown in the cool spring and fall months, but there are some varieties which will tolerate the heat of summer. Allow enough space between plants to insure the roots have enough space to develop.