Celestial Deadline

"Even the arts you call sorcery are governed by cosmic laws," answered the man in the green turban. "The stars direct these actions, as in other affairs. Not even my masters can alter the stars. Not until the heavens were in the proper order could they perform this necromancy."

—Robert E. Howard, People of the Black Circle

Magic doesn't obey human-made timepieces, but follows the cycles of nature and the movement of the spheres. A spell's duration, then, extends from sunrise to sunset, or during a phase in the lunar cycle, or some other vaguely fairytale measurement of time such as one's Dangerous Sixteenth Birthday or A Year and a Day or by following a celestial zodiac.

Comes in two varieties

Magic Has Dramatic Units of Time: Sunrise, sunset, twelfth gong of the clock-tower, the phases of the moon, birthdays, saint's days, Sabbath, etc. Which invokes all kinds of Fridge Logic, such as, what would use something so inaccurate as when the sun sets, especially since the world is round and there's always a sunset somewhere?
Magic Has Its Rules: Somehow setting limits such as a "Rule of Three" or "Until the Castle Rises Above the Clouds" or "Until the Sun Sets" makes the power work better or at all. So whatever happens needs to happen within the rules instead of at one's convenience. If a rules lawyer is around this sometimes leads to No Man of Woman Born.

If the events happen on their own after astronomical events, see When the Planets Align. Not to be confused with Cosmic Deadline. See Also Total Eclipse of the Plot.

Examples of Celestial Deadline include:

Anime & Manga

Inuyasha has a instance of being a human when the new moon comes around.
- Werewolves change during a full moon sometimes
Placing restrictions on Nen powers in Hunter X Hunter can act as a power multiplier for an ability, depending on the restriction.
In Nanatsuiro Drops, Tsuwabuki turns into a sheep plushie after sunset and changes back after sunrise. However, when the moon is full, he stays a plushie for a whole day, and during a new moon he stays human all day.
Angels and Demons who have not been fully trained in all magics in the manga Wish follow cycles. Angels are adult form during the day and chibi form during the night and demons are vice versa.

Fairy Tales

Bearskin must wear the bearskin for seven years.

Film

Ladyhawke: A couple is cursed so that she's a hawk by day and human by night, and he is human by day and a wolf by night. They only get to see each other in the moments of sunrise and sunset then were saved by Rules Lawyering
In Your Majesty, the evil wizard needs to perform a certain ritual with a virgin to create a dragon. This ritual may only be performed once every 100 years when the two moons align.
While not quite magical, in Once Upon a Forest, the heroes have only until "the moon is full" to collect the herbs and return them to save their friend Michelle.
In The Dark Crystal we have the Great Conjunction, an alignment of the world's three suns, described as a catalyst for "great change." In the film, the Dark Crystal must be completely reassembled and the Mystics and Skeksis reunited by the upcoming Great Conjunction in order for harmony to be restored.
Mogwai shall not be fed "after midnight", lest they turn into Gremlins. Nothing is said about when you can feed them again.
In the silent film The Golem, the Rabbi can only create the Golem while a certain astronomical constellation occurs. The occurence of another constellation supposedly causes the Golem to rebel.

Literature

In The Dresden Files universe, sunrise acts as a magical Reset Button. Many but the most powerful spells either fade completely or weaken considerably when the sun rises.
- Faerie magic likewise has this limitation. In Changes, Harry gets a whole panoply of goods from his faerie godmother, the Leanansidhe, but learns that they're only good until noon the next day.
Similarly, in the October Daye series, a number of spells dissipate at sunrise.
In Discworld, according to Death, The lawyers of Fate require a loophole. when dealing with prophecies.
Similarly, in A Game of Universe, the contract with the devil has a loophole: One year before it runs out, 13 heroes can be recruited to find the holy grail. If they find it before the contract runs out, the contract is nullified.
In Robert E. Howard's Conan the Barbarian story The People of the Black Circle, the king is killed by magic on a certain date.
In Robert E. Howard's Kull/Bran Mak Morn story "Kings of the Night", Kull's appearance is governed by this.

Out of the sunrise he came--into the sunset he has gone. Out of the mists of the ages he came to us, and back into the mists of the eons has he returned--to his own kingdom

In Adrian Tchaikovsky's Dragonfly Falling, Uctebri explains he is awaiting the most auspicious date.
In L. Jagi Lamplighter's Prospero Lost, Theo recommends that if they can't wait for a holiday, to use the Ouiji board on Wednesday. (Odin, and Hermes, the two gods associated with that day, were both associated with magic.)
In Edgar Rice Burroughs's The Monster Men, Chinese medicine is described as using this.

Tabletop Games

Changeling: The Lost: if you're lucky, contracts work until sunup or sundown, whichever happens first; or for free if you invoke Food Chains.
- also Pledges, Tokens, Goblins, and the True Fae.
Vampire: The Masquerade and Vampire: The Requiem both have a few powers, usually Blood Magic, that end at sunrise.
Dungeons and Dragons, around late 1st/early 2nd edition, would often include powers, usually magic items, that could be used "X times per day", but didn't define what the device considered "a day" (e.g., sunset, sunrise, 24 hours from the last use, etc.). This language was clarified in later editions.
- In the Dungeons and Dragons campaign world Ravenloft, adding a fanciful duration or an escape hatch when laying a curse makes it much more likely to take hold.

Theater

A Midsummer Night's Dream: The fairies show up When the Clock Strikes Twelve.

Puck: Now it is the time of night
That the graves all gaping wide,
Every one lets forth his sprite,
In the church-way paths to glide:
And we fairies, that do run
By the triple Hecate's team,
From the presence of the sun,
Following darkness like a dream,
Now are frolic:

Video Games

In Ghost Trick, the ghost Sissel is told that he will vanish from this world at dawn. It turns out that this is a lie to motivate him.

Web Comics

In Tales of the Questor, the hunt lasts until cockcrow. Not mind you, dawn. (Good thing for Exact Words.)
In Wapsi Square, 2012 is not only When the Planets Align, it's when you can do something about it.
In Dreamkeepers Prelude, Namah deduces her show's on as if it were this.
In Doodze, the sunlight only protects you as long as it's up.^{[dead link]}
In Erstwhile, the woman is allowed to go home only overnight.

Western Animation

The Little Mermaid: the contract is made until the sunset on the third day. Covering sunsets and the rule of three
Gargoyles They are stone during the day and flesh at night, in the film they are also cursed into dormancy "Until the Castle Rises Above the Clouds".
- Most magic in Gargoyles has similar limits. According to Word of God, adding any sort of "this spell goes away when X happens" condition, no matter how ridiculous it may sound, makes the spell much easier to cast successfully.
Sozin's Comet provides a boost to fire benders in Avatar: The Last Airbender. Also a solar eclipse causes firebenders to lose their fire bending completely during its duration (which is about 15 minutes).