8 P.M.
One of them slept while the others were on duty . The boys knew the time on shipboard , where the day begins at midnight , and is divided into watches of four hours each , thus making three watches for the night and three for the day . A bell is struck every half hour , so that each watch is noted by the eight strokes of the bell . What is called the dog-watches occur between 4 and 8 P.M. , this period being divided in the first dog-watch between 4 and 6 , and the second dog-watch between 6 and 8 . `` Why should such peculiar times be taken , or the periods be divided up in that way ? '' `` For the very reason that we discussed the arranging of our time of watch last night ; namely , so that one person would not have the same watch every night . It was agreed by us that one should have three hours ' uninterrupted sleep , while the others were on duty , so that each would in turn get three hours ' work .