Making time in the dungeon count, aside from food and resource consumption on behalf of the party, is important but also a potentially challenging thing to do. Here are a few examples which I’ll likely clean up later, which could be useful in making time matter within a dungeon.
The architects of this dungeon built small hollows which allow for the natural glow of moonlight to pour deep underground. Many rooms are sealed shut during the day, making a very narrow corridor of exploration built to lead tomb raiders into peril. As the moon rises and the sun sets, ceremonial cells and rooms for ancient caretakers open so that they might serve as custodians in the dungeon until the sun begins to rise and the moon begins to fall, when they will again return to their quarters. When the moon is at its apex, all doors sealed by Lunar Seals are opened.
On solstice days magical security systems are functioning at peak efficiency, though they lose the ability to distinguish between friend and foe; ignoring only those who wear moonstone amulets. They deal double the normal damage they normally would. Additionally on solstice days all doors that have Lunar seals are far easier to find, decreasing the difficulty by 1-in-6 from whatever the usual rate might be. They glow a faint blue.
During an eclipse these security systems are utterly disabled, allowing any wily thief to safely carve out the moonstone crystals that allow for the energy in the seals to power them. During these times however all doors will be sealed and unable to be opened short of using crowbars and extreme strength. There is no detectable hints of any hidden doors by way of errant moonlight, increasing the difficulty by 1-in-6 to determine hidden doors or to unlock them. Removing a power source moonstone leaves the object/door inert, unable to open, close, or function.
Who would use such a mechanism?
...A cult of ancient moon-worshippers who listened to the whispers beyond the void and basked in the pale light of the moon, their great hierophant buried in the bottom of the temple in a room one can only access on the solstice. Their ancient wards which use moonbeam shaft lights to detect movement and fire arrows laced with alien venoms are still active, and while their monks are dead and locked away behind sealed doors; at night the parasites that wrangle around their bones still bring them to venerate their forgotten masters.
...The Vampire of the Sapphire Pentacle, whose profane rituals are only of use in the pale blue light of a harvest moon. He slumbers away in his lunar sealed crypt until a perfect moonrise when the locks and seals open to give him full use of his ritual laboratories. His insectoid henchmen remain in hibernation until intruders arrive, and any who pass by a moonstone eye embossment are sensed by the creatures.
The Thieves Guild of Munghala Bhat, who venerate the Vagabond Goddess they call the Starry-Eyed Walker. The slums of Munghala Bhat run with frescos and moonstone embossments that shift into openings, hidey-holes, alcoves, weapon caches, and murder caches that only senior brothers of the thuggee group are given full knowledge of. Guards who tarry too long in put behind the frescos and left to the slow death of suffocating during the sunny jungle day.
Everyone in a dungeon has to eat, especially those who are on patrol or busy busting their humps trying to fight the PCs. While the examples present here might be useful for Orcs, Ogres, and Goblins; they work just as well for stereotypically thuggish and stupid human guards. This should be an easy one, commonly used.
One hour prior to the Feasting Hour, those on patrol in the dungeon start to get angrier than usual due to a lack of warm fleshy goodness in their guts. Nobody wants to die with an empty gut, so in combat their morale is halved, but their damage is upgraded by one degree of dice (until they fail a Morale check, just in case the party wanted to confront them again while they run off for help/to change shift).
If the party enters the Feasting Hall during a Feasting Hour, there’s a 1-in-6 chance of the enemy forces noticing the party if they’re just sneaking through. They’re hungry, they’re pissed, they are making a sloppy mess. Think of a cafeteria of slovenly orcs slinging gruel and pig skin every which way as they feast their hearts out and bitch about their day. They’ll share in rumors, loudly, because everyone likes to gossip; but any rumor will be responded to with inconclusive statements such as “You’re full of it!” or “Shuttit ya goon!” or “I hear that!” which really doesn’t make the information reliable. If the party is not in disguise, or actively tries to engage with the feasting group, the rate of discovery is upped by +1-in-6 for each; as it might cause the feasters to look up and see who is talking to them weird-like.
If the party tries to get into combat with feasting enemies, they do not suffer any need to roll Morale until more than half of them are dead, and the party has a chance of infection with every wound they take---nobody knows how fresh the food is or what the cook was putting into it.
Fighting a group of enemies who have just feasted puts the party at an advantage. Such enemies have +1d4 Hit Points, but they are in a logy stupor and suffer an equal penalty to their To Hit rating. A critical hit with a bludgeoning weapon will cause them to upchuck their meal violently, sickening them for 1d4 rounds.
Where might this be applicable?
...The Orc-Hold, which is suffering from a lot of disgruntled marauders due to their warlord trying to act all smart-like for the drow elves a few floors beneath the surface of the world. The orcs just want to eat and be done with it because each day is a mark against their honor, and the drow elf food they’ve been getting tastes like crap but ol’cookie knows how to salt it so it atleast takes like man-flesh; rather than worm-man-flesh.
...The gaol of Lord Gunderhall, who was never known for employing the best and brightest; rather usually employing the girthiest and most sadistic. His men want to get drunk and feast on dry breads and fat hams. All they do is tell bawdy tales while they feast, and they seldom ever look up from the table unless a pretty lady is talking to them. They’re exceptionally cruel and craven if caught before their supper, and the prisoners know better than to rile up any trouble during that period of time lest they be beaten toothless.
Sometimes verticality can be nice. In this case, imagine a giant underground cavern with metal wheels hanging from great chains and ceilings, usually above gigantic abysses of darkness that lead several hundreds of feet down. By playing with chains and locks, one can flood the dungeon with water from a nearby lake or sea, increasing the threat level of monsters within the dungeon, but also drying out the seabed nearby which will allow for a secret escape route. The tides can play into making the escape route and the flood gates accessible or not, as can storms.
In the event of a storm, the wheels will spin with water and begin flooding the dungeon regardless. The party will need to keep track of the rate of water rising (about 1 foot every minute) which will begin by filling up the deep abyss, and then the dungeon proper. Monsters from the deep abyss will rise and pursue the party, and the usual way of draining and playing with the flood locks will no longer function; it’ll just increase the rate of water and allow the creatures to approach the party faster.
Working without a storm and then working against a storm in the same run allows for an interesting dynamic, as the party is first in charge of opening floodgates to access new areas, and then forced to seal flood gates and locks to prevent the water from rising beyond their own control once the storm moves in. An intelligent enemy could use the wheels and locks against them and unless the party is aware of the storm outside, that flight to the nearby seabed escape hatch could lead them to flooding the dungeon further and drowning on their way out.
Who might use such a contraption?
...The Deep Ones, likely hiding it under a water mill to obscure its true purpose. The abyssal reavers of the deep seaside catacombs come up when the waters are high and feast upon unworthy sacrifices, fornicating with those they deem worthy of their progeny. The strewn belongings of countless dead linger on the abyssal bed, and proper manipulation of the flood locks could see the party descend to a safe-enough depth to skim the gold off the bottom and deal with these fish beasts in only a few feet of water’s depth. But a storm, which is common along this seaside town, can turn a profitable and advantageous venture to a perilous endeavour quickly.
...The Ghoul Vicar of the Hellmouth of Wrath, who built his dungeon into the flesh of a titan. Rather than water it is blood, and the wheels and chains are bladed and sharp; but the lurking threat of the down below takes the form of giant parasites and lesser ghouls. During a blood rain, which is common enough in Hell, the Titan’s body stirs and pumps blood all on its own, causing greater problems than the usual for those locked within its body. But the treasures of ancient titanic power and the arcane reagents of the Hellish Dead are worth the risk to those strong enough to deem themselves harvesters.
While obviously these examples aren’t the greatest, they do add some tactical value in being aware of the time you’re in the dungeon and of what is going on outside the dungeon. Which can be useful in making the dungeon not feel too removed from the rest of the game-world proper.