Set Form item label on top only for group of component ?

Flow
1

I want to group vertically a listBox and checkbox in a FormLayout…

this is my snippet :

addFormItem(                    
	new VerticalLayout() {{
                        
		add(
			new DatePicker() {{
					setRequired(true);
					getBinder().forField(this)
                    .withValidator(Objects::nonNull, " The start at should be defined")
                    .bind(... )
		}});
		add(new Checkbox("Immediately start"));
        }},
		"Start at:"
      );

but the item label display on the middle not on the top…

how to make label form on top OR maybe in the middle of DatePicker startAt :
17369533.png