The Children of the King by F. Marion Crawford

Ruggiero found out before long that his master for the summer was eccentric in his habits, judging from the Sorrentine point of view in regard to order and punctuality. Ruggiero's experience of fine gentlemen was limited indeed, but he could not believe that they all behaved like San Miniato, whose temper was apparently as changeable as his tastes. Sometimes he went to bed at nine o'clock and rose at dawn. Sometimes on the other hand he got up at seven in the evening and went to bed by daylight. Sometimes everything Ruggiero did was right, and sometimes everything was wrong. There were days when the Count could not be induced to move from the Marchesa di Mola's terrace between noon and midnight or later, and again there were days when he went off in his boat in the morning and did not return until the last stragglers on the terrace of the hotel were ready to go to bed. He was irregular even in playing, which was after all his chief pastime.

Possibly he knew of reasons why it should be good to gamble on one day and not upon another.