nine o'clock
By the time that all the tasks had been performed the boys were glad to lie down on the grass and rest until it was time to prepare a light supper . After that meal was over Dave asked : `` We 're going to keep regular guard to-night , are n't we ? '' `` Yes , '' Dick answered . `` We 'll turn in at nine o'clock and keep guard until six in the morning . That will be nine hours -- an hour and a half of guard duty for each fellow . Suppose we draw lots to decide the order in which we shall take our tricks of guard duty . '' This was done .