Set the system time and date

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;