var
  OldTime: TDateTime = 0.0;
  OldTick: UInt64;
  Times: TArray<TDateTime>;
begin
  try
    OldTick := GetTickCount64;
    repeat
      if Now <> OldTime then
      begin
        Times := Times + [Now];
        OldTime := Now;
      end;
    until GetTickCount64 > OldTick + 20;

    WriteLn;

    for var I := Low(Times) to High(Times) do
      WriteLn(I:5, ' = ', FormatDateTime('hh:nn:ss.zzz', Times[I]));

    ReadLn;
  except
    on E: Exception do
      WriteLn(E.ClassName, ': ', E.Message);
  end;
end.

    0 = 12:14:49.512
    1 = 12:14:49.513
    2 = 12:14:49.514
    3 = 12:14:49.515
    4 = 12:14:49.516
    5 = 12:14:49.517
    6 = 12:14:49.518
    7 = 12:14:49.519
    8 = 12:14:49.520
    9 = 12:14:49.521
   10 = 12:14:49.522
   11 = 12:14:49.523
   12 = 12:14:49.524
   13 = 12:14:49.525
   14 = 12:14:49.526
   15 = 12:14:49.527
   16 = 12:14:49.528
   17 = 12:14:49.529
   18 = 12:14:49.530
   19 = 12:14:49.531
   20 = 12:14:49.532
   21 = 12:14:49.533
   22 = 12:14:49.534
   23 = 12:14:49.535
   24 = 12:14:49.536
   25 = 12:14:49.537