First parameter of SetWindowText is hwnd, not control identifier. Try this:
SetDlgItemTextW(hWnd, 1003, dateStr);
Use this for retrieve date:
WCHAR dateStr[256] = {0};
_wstrdate(dateStr);
Also use wide string parameters for CreateWindow:
hwndLabel = CreateWindowW(L"STATIC",L"Time",
WS_VISIBLE | WS_CHILD | SS_RIGHT,
10,200,75,35,hWnd, (HMENU)1003, NULL, NULL);