In the schema definition you can indicate that a node value is limited to Day or Night. These are the only two valid values that are allowed. When that gets inported into Designer we will create a dropdown list with the two values in it. There is no indication that you want a radio button, so you will have to go and adjust this after you import.
You can indicate what you want for the ON/Off values in the binding tab of the radiobuttonList. In Your case the On value for one radio button will be "Day" and the On Value for the other will be "Night". By querying the RadioButtonList it will tell you which one is On.