This message occurs when an application makes a change (or set of changes) to the system time. Any application that changes the system time should send this message to all top-level windows.
wParam
This parameter is not used.
lParam
This parameter is not used.
To send the WM_TIMECHANGE message to all top-level windows, an application can use the SendMessage function with the hWnd parameter set to 0xFFFF.
SendMessage