Create TimeSpan values for the values, then you can simply do arithmetic with them. Example:
TimeSpan start = new TimeSpane(9, 30, 0);
TimeSpan stop = new TimeSpan(21, 30, 0);
TimeSpan interval = new TimeSpan(0, 30, 0);
for (TimeSpan s = start; s <= stop; s += interval) {
Console.WriteLine(s.ToString());
}
--- single minded; short sighted; long gone;