For the characters, time is not measured in the real time of the players around the gaming table. Time may pass faster or slower in the game world, even to the extent of the GM's mentioning, for example, “a month passes.” Game time is measured in turns (10 minutes), rounds (1 minute) and segments (six seconds). Unless the party is engaged in combat, almost all game time in dungeons is measured in the 10-minute turn.
The GM normally records the passage of time, but a few GMs delegate keeping track of time to a particularly trustworthy player.
Measuring time can be important for many reasons; torches burn down to useless stubs, food is consumed, and wounded characters heal damage as they rest. In dangerous environments, such as wildernesses or dungeons, the GM will typically make periodic checks to see if any “wandering monsters” appear. These checks are normally carried out every so many turns, or hours, or days. Since wandering monsters rarely have treasure, the appearance of wandering monsters serves to reward characters who do not waste time (or more accurately, to punish those who do). See “Exploring the Dungeon” for more on this.