You could use it like:

Code:
var
  strings: TStringList;
begin
  strings := TStringList.Create;
  strings.LoadFromFile('timer.txt');
  
  // to change a value at index 0
  strings[0] := 'new value';

  // to delete a value at index 0
  strings.Delete(0);

  strings.SaveToFile('timer.txt');
  strings.Free;
end;