private void rbTime_Click(object sender, EventArgs e)
  {
      if (rbTime.Checked == true)
      {
         rbTime.Checked = false;
      }
      else if (rbTime.Checked == false)
      {
         rbTime.Checked = true;
      }
 }

 //局部变量
private bool rbcheck = true;

if (rbcheck)
   {
        rbTime.Checked = false;
        rbcheck = false;
   }
else
  {
        rbTime.Checked = true;
        rbcheck = true;
   }