ten P.M.
`` Rattly Robot , '' a dull-witted mechanical clod who was continually falling over himself and getting into trouble . It was a repellent caricature , but could still be very funny . Jon was just starting to read it when the ceiling light went out . It was ten P.M. , curfew hour for robots . Lights out and lock yourself in until six in the morning , eight hours of boredom and darkness for all except the few night workers . But there were ways of getting around the letter of a law that did n't concern itself with a definition of visible light . Sliding aside some of the shielding around his atomic generator , Jon turned up the gain .