Try this:
private void populateDropdown(ComboBox dropdown, DateTime startTime, DateTime endTime, TimeSpan interval)
{
dropdown.Items.Clear();
DateTime time = startTime;
while (time <= endTime)
{
dropdown.Items.Add(time.ToString("HH:mm tt"));
time = time.Add(interval);
}
}
Then call it like this:
populateDropdown(comboBox1, new DateTime(2000, 1, 1, 8, 0, 0), new DateTime(2000, 1, 1, 12, 30, 0), new TimeSpan(0, 30, 0));