Bearing An Hourglass: Piers Anthony

Book II of Incarnations of Immortality. In a world where physics and magic flow side by side, the Incarnation of Time is a potentially powerful figure. But Chronos is fated to perform his task backwards: he begins his career at its end - as a complete novice, ill-equipped to cope with the subtle schemes of Satan, Father of Lies and Illusion. It was after the death of the child he had fathered and the suicide of the woman he loved, that Norton accepted the role of time and took up the power-filled hourglass. But his terrible loss, combined with his awesome capabilities, makes him peculiarly vulnerable to Satan's wiles.