What does the watchdog do in the fantasy world that Milo has entered?

The watchdog asked Milo what he was doing in the Doldrums. They are the guardians of time, continuously on the lookout for whoever is wasting time.

Explanation:

The Phantom Tollbooth is a fantasy story written by Norton Juster that tells the story of a young boy named Milo. The plot revolves around the imaginary Kingdom of Wisdom and Milo's experience in the kingdom.

The watchdog is the guardian of time, looking for anyone who wastes time. When Milo entered the fantasy world, the watchdog asked him what he was doing in the Doldrums. Milo replied that he was just "killing time", that led to the watchdog's anger, leading him to furiously tell him that killing time is worse than wasting time.