How to see TTimer interval

What do you mean by seeing the Timer interval?
If you set the timer interval to 1000 ms (1 second) then:

Edit1.Text := IntToStr(Timer1.Interval);

Select allOpen in new window

For counting down:

var  // global variable
  i:integer=20; // the number that you want to count down from
...
procedure TForm1.Timer1Timer(Sender: TObject);
begin
  Edit1.Text := IntToStr(i);
  dec(i);
  If i = 0 then
    Timer1.Enabled := False; // to stop counting
end;

Select allOpen in new window

If i set timer interval to 10000 ms. On timer event after 10 s specific code will be executed.

A need to know  how much time i have less until timer time will be elapsed.

Ok, thank you.

Can You explain me just another thing.

Will timer event on interval interrupt another  task which was running at that moment.
And the task will continue after timer code will be executed?

>> Will timer event on interval interrupt another  task which was running at that moment.
No, whatever you have in the Timer event will run concurrently with the other code that you might have.
For example if you have ListBox, Button and Timer on a form: The Timer running as per the above code and you have pressed a button that has the following code:

procedure TForm1.Button1Click(Sender: TObject);
var
  j:integer;
begin
  for j := 1 to 30000 do
    begin
      ListBox1.Items.Add(inttostr(j));
      ListBox1.Selected[ListBox1.Items.Count-1] := true;
      Application.ProcessMessages;
    end;
end;

Select allOpen in new window

Then you get the Timer count down while the ListBox adds the loop counter.

Thank you very much

Try next code with two TListbox, TButon and TTimer.
They are not ruining   together?

procedure TForm4.Button1Click(Sender: TObject);
var
  j:integer;
begin
//timer1.Enabled:=false;
  for j := 1 to 30000 do
    begin
      ListBox1.Items.Add(inttostr(j));
      ListBox1.Selected[ListBox1.Items.Count-1] := true;
      Application.ProcessMessages;
    end;
end;

procedure TForm4.Timer1Timer(Sender: TObject);
var
  k:integer;
begin
  for k := 1 to 30000 do
    begin
      ListBox2.Items.Add(inttostr(k));
      ListBox2.Selected[ListBox2.Items.Count-1] := true;
      Application.ProcessMessages;
    end;
end;

Select allOpen in new window

pleas use also in attached code below:
timer1.Enabled:=false;

procedure TForm4.Timer1Timer(Sender: TObject);
var
  k:integer;
begin
 timer1.Enabled:=false;
  for k := 1 to 30000 do
    begin
      ListBox2.Items.Add(inttostr(k));
      ListBox2.Selected[ListBox2.Items.Count-1] := true;
      Application.ProcessMessages;
    end;

end;
end.

Select allOpen in new window

not really the way to go, and especially not with application.processmessages

the article i wrote about the progressbar and a thread should be a lot better than this

I should have been more clear on my answer about the concurrent processing through the Timer.
Timer can work concurrently (as i shown in my last post) but it can not work like threads. Timer can accomplish Background Processing or Multitasking but it can not perform Multithreading.

I understand.
Now is not necsessary  for me to study Multithreading.

(But sill it would be of help if i could see how much time remains of timer time in TEdit
(like count down).)

Thank you