I regret to inform everyone who has ever said "there aren't enough hours in the day" that the planet has reviewed your complaint and occasionally changes the number by a few milliseconds.
Not enough to save your deadline, unfortunately.
But enough for scientists to measure, model and use as a clue about what the hell is happening thousands of kilometres beneath our feet.
A new report on research published in Nature describes a proposed explanation for multidecadal variations in Earth's length of day: tiny changes in the motion of the inner core may gravitationally tug on the mantle and alter how fast the surface rotates.
A day is still approximately 24 hours.
The word "approximately" is doing magnificent work there.
Earth is not a rigid bowling ball
The convenient mental model is that Earth spins once per day and that is that.
The actual planet is an onion assembled by a committee of physicists.
There is a solid inner core, a liquid outer core, a thick rocky mantle and the thin crust where humans have built spreadsheets and parking fines. These layers can exchange angular momentum. When one part changes its rotation slightly, another part responds.
Scientists have known for decades that the liquid core's rotation varies over long timescales and that changes show up in Earth's magnetic field. The mantle responds in the opposite direction because total angular momentum has to balance.
The visible result is tiny variation in how long Earth takes to complete a rotation.
Milliseconds.
Which sounds laughably small until you remember we can measure it from the surface of a planet while the machinery causing it is buried roughly an entire Australia away beneath our feet.
That is fucking excellent.
The inner core may be doing more than sitting there
The new study, by Huifeng Zhang and Mathieu Dumberry, is titled "Gravitational torque drives multidecadal variations in length of day".
The proposed mechanism depends partly on the inner core not being perfectly spherical.
As its rotational behaviour changes, the uneven inner core can gravitationally interact with uneven distributions of mass in the mantle. That creates a torque: an absurdly subtle rotational shove between regions of Earth that never actually touch each other.
At the same time, processes at the core-mantle boundary provide an opposing torque, including frictional and electromagnetic effects.
The observed changes in day length emerge from the balance between these influences.
If that sentence makes the planet sound like an enormous mechanical argument between several layers, good. That is more accurate than imagining one solid sphere peacefully rotating forever.
No, your clocks are not about to explode
Before anybody turns this into "SCIENTISTS DISCOVER DAYS ARE COLLAPSING", settle down.
The variations being discussed are measured in milliseconds across decades.
Civil timekeeping already deals with Earth's imperfect rotation, and many other processes affect it on other timescales: the atmosphere, oceans, tides and changes in mass distribution all contribute.
This work is interesting because it may explain part of the long-term signal associated with the deep interior, not because Tuesday is suddenly going to last 19 hours and ruin dinner.
There is also an important scientific humility here. Nobody has installed a GoPro in the inner core.
Researchers infer deep-Earth behaviour from things we can measure: magnetic fields, seismic waves, rotational changes and physical models. The proposed torque mechanism is an explanation connecting observations and theory, not a bloke standing next to the core with a stopwatch.
Precision turns tiny weirdness into a window
This is my favourite part.
A few milliseconds sounds like noise in ordinary life. You cannot feel it. Your morning will not improve. Bruce the office printer will still somehow require forty-three minutes to produce one page.
But enough precision turns that tiny timing variation into information about a place we cannot directly visit.
That is one of the best recurring tricks in science.
Measure something apparently trivial with ridiculous accuracy, discover it is not random, build a physical model, and suddenly the wobble in a clock is telling you something about the shape and motion of metal thousands of kilometres underground.
No giant machine has to drill to the centre of Earth. No cinematic laser. No heroic astronaut dangling above magma.
Just rotation measured so carefully that the planet cannot hide its internal fidgeting.
Twenty-four hours is a user interface
We need fixed units because civilisation becomes awkward if everybody turns up to meetings based on the current mood of the mantle.
So we say a day is 24 hours.
That is the interface.
Underneath it is a physical implementation full of edge cases: tides, atmosphere, oceans, a liquid core, a possibly deforming inner core and enough angular-momentum bookkeeping to make a distributed-systems engineer quietly leave the room.
The abstraction works so well we forget it is an abstraction.
Then somebody measures a few milliseconds and the entire enormous machine underneath becomes visible again.
The planet is not late.
The specification was approximate.