private DateTimePicker _timePortionDateTimePicker;
private DateTime _pickedTime;
private bool btnWasClicked = false;
private bool timeChanged = false;

private void TimeIsChanged(object sender, EventArgs e)
{
  timeChanged = true;
  if (timeChanged)
  {
    btnWasClicked = true;
  }
}

private void BtnChangeTime_OnClick(object sender, EventArgs e)
{
  Form timeDialog = new Form();

  _timePortionDateTimePicker = new DateTimePicker();
  _timePortionDateTimePicker.Format = DateTimePickerFormat.Time;
  _timePortionDateTimePicker.ShowUpDown = true;
  _timePortionDateTimePicker.ValueChanged += new
                                             EventHandler(TimeIsChanged);

  timeDialog.Controls.Add(_timePortionDateTimePicker);
  timeDialog.ShowDialog();

  _pickedTime = _timePortionDateTimePicker.Value;
}