It shall be lawful for the court to allow the United States attorney to amend his statement of complaint at any stage of the proceedings, before verdict, if, in the opinion of the court, such amendment will work no injustice to the accused; and if it appears to the court that the accused is unprepared to meet the charge as amended, and that an adjournment of the cause will promote the ends of justice, such adjournment shall be made, until a further day, to be fixed by the court.