uses DateUtils;
.
public
  { Public declarations }
  jam: TTime;
.
procedure TForm1.Button1Click(Sender: TObject);
begin
  jam:= IncMinute(jam, 10);
  Edit1.Text:= TimeToStr(jam);
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
  jam := now;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  jam:= IncMinute(Now, 10); // --> modified here
  Edit1.Text:= TimeToStr(jam);
end;

@anak_s0leh: nah pada saat saya klik 1 jam kemudia, program saya malah nambahkan hasil pada proses ke dua, pengennya jam = jam_sekarang + 10 menit; mohon solusinya...

uses DateUtils;
.
public
  { Public declarations }
  jam: TTime;
.
procedure TForm1.Button1Click(Sender: TObject);
begin
  if HoursBetween(jam, now) >= 1 then  jam:=now;
  jam:=IncMinute(jam, 10);
  Edit1.Text:= TimeToStr(jam);
end;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
  jam := now;
end;