[Страдалецъ]

Я такое делал, только у меня в обратную сторону к 00:00:00 считало, для вас адаптировал:

Код:

unit Unit10;

interface

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

type
  TForm10 = class(TForm)
    Timer1: TTimer;
    Label1: TLabel;
    procedure Timer1Timer(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
   LeftSeconds: Integer;
  public
    { Public declarations }
  end;

var
  Form10: TForm10;

implementation

{$R *.dfm}

procedure TForm10.FormCreate(Sender: TObject);
begin
 LeftSeconds := 3600*24-5;
end;

procedure TForm10.Timer1Timer(Sender: TObject);
Var H, M, S: String;
    T: Integer;
begin
 T := LeftSeconds;
 H := IntToStr(T div 3600);
 Dec(T, T div 3600 * 3600);
 M := IntToStr(T div 60);
 Dec(T, T div 60 * 60);
 S := IntToStr(T mod 60);

 if Length(H) = 1 then H := '0'+ H;
 if Length(M) = 1 then M := '0'+ M;
 if Length(S) = 1 then S := '0'+ S;
 Label1.Caption := H + ':' + M + ':' + S;
 Inc(LeftSeconds);
end;

Код:

object Form10: TForm10
  Left = 0
  Top = 0
  Caption = 'Form10'
  ClientHeight = 137
  ClientWidth = 406
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  OnCreate = FormCreate
  PixelsPerInch = 96
  TextHeight = 13
  object Label1: TLabel
    Left = 128
    Top = 40
    Width = 146
    Height = 45
    Caption = '00:00:00'
    Font.Charset = DEFAULT_CHARSET
    Font.Color = clWindowText
    Font.Height = -37
    Font.Name = 'Tahoma'
    Font.Style = []
    ParentFont = False
  end
  object Timer1: TTimer
    Interval = 5
    OnTimer = Timer1Timer
    Left = 80
    Top = 8
  end
end