This function stops a timer.

#define INCL_WINTIMER /* Or use INCL_WIN, INCL_PM, */
#include <os2.h>

HAB      hab;      /*  Anchor-block handle. */
HWND     hwnd;     /*  Window handle. */
ULONG    ulTimer;  /*  Timer identifier. */
BOOL     rc;       /*  Success indicator. */

rc = WinStopTimer(hab, hwnd, ulTimer);