An application sends a ZGM_SETCELLCDATE message to set the specified cell in the ZeeGrid to the date specified by the null-terminated string in lParam.
ZGM_SETCELLCDATE
wParam = (WPARAM)(int) iCellIndex; //Cell index
lParam = (LPARAM) lpszString; //pointer to string representation of a date
Valid dates range from 1/1/1600 to 12/31/9999.
If the string representation of the date specified in lParam can be deciphered into a valid date, the message will return the julian date of the specified string date.