Use SystemTime structure for changing system date and time, and then use SetSystemTime procedure to set them into the system.
procedure TForm1.Button1Click(Sender: TObject); var dt: TSystemTime; begin dt.wYear:=1999; dt.wMonth:=2; dt.wDay:=25; dt.wHour:=9; dt.wMinute:=0; dt.wSecond:=0; dt.wMilliseconds:=0; if SetSystemTime(dt) then Label1.Caption:='Setting finished'; end;