function GetWinUpTime: String;

const
  Days: Integer = 1000 * 60 * 60 * 24;
  Hours: Integer = 1000 * 60 * 60;
  Minutes: Integer = 1000 * 60;
  Seconds: Integer = 1000;

var
  iTicks, iDay, iHour, iMin, iSec: Integer;
begin
  iTicks := GetTickCount;
  iDay := iTicks div Days; //Tage
  Dec(iTicks, iDay * Days);
  iHour := iTicks div Hours; //Stunden
  Dec(iTicks, iHour * Hours);
  iMin := iTicks div Minutes; //Minuten
  Dec(iTicks, iMin * Minutes);
  iSec := iTicks div Seconds; //Sekunden
  Result := IntToStr(iDay) + ' Tage, ' +
            IntToStr(iHour) + ' Stunden, ' +
            IntToStr(iMin) + ' Minuten, ' +
            IntToStr(iSec) + ' Sekunden';
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowMessage(GetWinUpTime);
end;