An application sends the WM_TIMECHANGE message to all top-level windows after changing the system time.
WM_TIMECHANGE wParam = 0; // not used, must be zero lParam = 0; // not used, must be zero
This message has no parameters.
An application should return zero if it processes this message.
An application that changes the system time should send this message to all top-level windows. To send the WM_TIMECHANGE message to all top-level windows, an application can use the SendMessage function with the hwnd parameter set to HWND_TOPMOST.