
const
  SecPerDay = 86400;
  SecPerHour = 3600;
  SecPerMinute = 60;

function SecondToTime(const Seconds: Cardinal): Double;
var
  ms, ss, mm, hh, dd: Cardinal;
begin
  dd := Seconds div SecPerDay;
  hh := (Seconds mod SecPerDay) div SecPerHour;
  mm := ((Seconds mod SecPerDay) mod SecPerHour) div SecPerMinute;
  ss := ((Seconds mod SecPerDay) mod SecPerHour) mod SecPerMinute;
  ms := 0;
  Result := dd + EncodeTime(hh, mm, ss, ms);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  label1.Caption := DateTimeToStr(Date + SecondToTime(12543));
end;