On game time and what causes advancement of the hunger/thirst/fatigue bars:
There are two different "clocks" that indicate when "time" is advancing in the game. The first clock (the "bar clock") is when actions you perform cause your hunger/thirst/fatigue bars to advance. The second clock (the "world clock") is the advancement of the day-night cycle, and also includes plant growth and creature movement. Both of these "clocks" are paused while you stay remain in your character or inventory screens, or avoid performing actions that drop you out to the game world. Thus both making tools and converting sheafs of wheat into grain while inside the inventory screen are done with both clocks paused.
On the other hand, eating food, frying meat, making cord, and opening clams all momentarily drop you out of the inventory screen into the game world, so those actions cause world time to advance. The rule is that if the bar clock is advancing, the world clock is always advancing as well, but the reverse is not true; both looking around while standing in one place and building structures advance the world clock but not the bar clock. This distinction between the different clocks is important in the game, because the bar clock rules when you must eat, drink, or sleep, while the world clock has less effect on your game play (it still has some effect, such as spawning new creatures or fruit and the loss of vision you experience at night). It is quite possible to leave your character parked in a safe location, walk away from the game for several hours, and return to find none of the hunger/thirst/fatigue bars have moved but all your planted grain has matured and new animals and fruit have spawned, several days have passed, and it has gone from night to daylight. Unless you are in a dangerous location (drowning under water or being attacked by some animal), stumbling around in the dark can always be avoided in this way by just waiting a while until daybreak.
Some actions cause a bigger change to your bars than others; which actions do so appears be somewhat intuitive; not moving (except for looking around) doesn't effect the bars at all, running has a light effect, and heavy labor such as digging, breaking rocks, (and apparently fishing) tend to cause the fastest increase in hunger, thirst, and fatigue.