Forced March
In a day of normal walking, you walk for 8 hours, and then you spend the rest of your daylight time making and breaking camp, resting, and eating. However, you can walk for more than 8 hours in a day by making a forced march. For each hour of marching beyond 8 hours, you must succeed at a Constitution check (DC = 10 + 2 per extra hour) or you take 1d6 nonlethal damage. If you take any nonlethal damage from a forced march, you become fatigued (see page 276). When you recover from this nonlethal damage, you also eliminate the fatigued condition. Still, it’s quite possible to march yourself into unconsciousness by pushing yourself too hard.
Source
Core Rulebook pg. 258