The riddle “What time is it when an elephant sits on a fence?” is a playful and humorous question. The answer, “It’s time to fix the fence,” is a joke based on the idea that an elephant is so large and heavy that it would undoubtedly break any fence it sits on. Therefore, if an elephant sits on a fence, it is time to repair it because the fence would be damaged by the elephant’s weight. The humor comes from the unexpected and exaggerated scenario.