Update-Clock

Yes, you can use a timer (with the rate about a half of the smallest unit, so in this case ~500ms) and update your clock box from the CYourDialog::OnTimer(..) directly, by your code above :) (the actual time will be set to a DateTimePicker at its creation, you could initialize your box in CYourDialog::OnInitDialog() for the first time only, then start the timer and let it work)

Your track is correct :)

void CYourDialog::UpdateClock()
{
CString cszTime;
// Format the string with the date/time information here...
// ...

GetDlgItem(IDC_STATIC_CLOCK)->SetWindowText(cszTime);
}

void CYourDialog::OnTimer(UINT_PTR uiEvent)
{
UpdateClock(); // nothing more

CDialog::OnTimer(uiEvent);
}

int CYourDialog::OnInitDialog()
{
int iResult = CDialog::OnInitDialog();

UpdateClock();

/*UINT_PTR dialog member*/ m_uiTimer = SetTimer(1, 500, 0);

return iResult;
}

void CYourDialog::OnDestroy()
{
KillTimer(m_uiTimer);
}

Please control also your message map implementation:

BEGIN_MESSAGE_MAP(CYourDialog, CDialog)
ON_WM_TIMER()
ON_WM_DESTROY()
...
END_MESSAGE_MAP()