twelve o'clock
`` We 'll do more than that , '' said Sam . `` We 'll have somebody on the lookout . I guess it would n't be very much of a job for you boys to divide the night up into watches . I 'll stay on duty until eleven or twelve o'clock and from then on until six would n't take more than an hour and a half from each of you . '' `` We 'll do that , '' said Fred quickly . `` That 's a good suggestion , Sam . '' `` But if we have the Black Growler fast inside the boat-house how can any one get at her ? ''