procedure
TForm1.Button1Click(Sender: TObject);
var
 i: Integer;
begin
for i := Planner1.Display.DisplayStart to Planner1.Display.DisplayEnd do
 begin
   if not Assigned(Planner1.Items.FindFirst(i,i + 1,0)) then
   begin
     with Planner1.CreateItem do
     begin
       ItemBegin := i;
       ItemEnd := i + 1;
       ItemPos := 0;
       Text.Text := 'first empty';
       CaptionType := ctNone;
     end;
     break;
   end;
 end;
end;