Radishes are very hardy. They can go to seed though I have never seen it happen myself. I have myself tried them indoors for the first time and they seem to be doing very very well. I notice they look to be stretching a bit and have laid over like a vine. This shouldnt make a diffrence though. As for when to pick, well you will be looking at the tops of the radishes for a while as they mature. Depending on the type they will look a little diffrent on the surface. All my outdoor grows taut me to expect about 1/4 - 1/3 of the radish to stickout of the ground. I am going to buy some German Giants pretty soon and try those.. they are monsters, some as big as tennis balls and with a nice bite.
I am currently giving these radishes a half dose of nutes since my soil is pretty rich as it is.. I use a Turkey baster to water them as well as my other things that I want to do precission watering on. Here is a pic of the setup where you see the old Oil Tub, thats where I planted my radishes. And before I get flammed..lol.. the tub was never used for more than to ice down beer during BBQ's
I will post a current pic for you when I get a chance.. the lights are 600w each and much closer now that the sprouts are around 3" high.