ten o'clock
I agree to your plan at once . '' `` All right , then . We have no time to lose . It is half-past ten o'clock now . At twelve supper will be served , when all the guests will lay aside their masks . So you see that we have but an hour and a half to effect our change of dress and hoax our wise companions . Just before supper we must slip up here again and change back , so that we may unmask at supper in our proper disguises . ''