unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls, StdCtrls, Funcoes;

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Edit2: TEdit;
    Button1: TButton;
    Panel1: TPanel;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

Function AcumulaTempo(Hora1,Hora2:String):String;
var
   hora,min,seg:integer;
begin
     hora:=strtoint(Copy(Hora1,1,2))+strtoint(Copy(Hora2,1,2));
     min:=strtoint(Copy(Hora1,4,2))+strtoint(Copy(Hora2,4,2));
     seg:=strtoint(Copy(Hora1,7,2))+strtoint(Copy(Hora2,7,2));

     if seg>=60 then
      begin
       min:=min + seg div 60;
       seg:=seg mod 60;
      end;

     if min>=60 then
      begin
       hora:=hora + min div 60;
       min:=min mod 60;
      end;

     if hora > 99 then
      Result:=Format('%.3d:%.2d:%.2d',[Hora,min,seg])
     else
      Result:=Format('%.2d:%.2d:%.2d',[Hora,min,seg]);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
     Panel1.Caption:=AcumulaTempo(Edit1.Text,Edit2.Text);
end;

end.

Observação: Por: David sapodiou2@bol.com.br