The problem is, one of the first things you do when you make dandelion wine is throw away the flowers.

Seventeen minutes. That's how long the world lasts this time.
The crucifixes with their screaming human sacrifices flayed and nailed to the i-beam crosses vanish, replaced by a bucolic pastoral scene, the serenity of the gold-flecked, rolling hills ruined only by the presence of a thirty foot tall Albertosaurus biting the head off a three-headed sheep. He hits the stopwatch, resets the timer. 00:00:01 and counting.
He decides to head south, pushing through the fields of waist-high dandelions and away from the predator messily devouring its meal. A throbbing scar on his leg, angry and red, serves as a reminder that a few minutes are long enough to be maimed or killed. He takes a moment, once he is far enough from the gory scene, to tear the leaves off of one of the plants and cram them into his mouth. They taste bitter, and tough, but they are edible, and he has not eaten in a long time.

They told him that he would be safe. They told him that he needed to carry the information across the universes. Somewhere out there, they said, there would be a universe where the Foundation still existed. Find them, tell them what happened. Maybe they can fix it.

He tears the stem off of one of the oversized dandelions and sucks on the milky sap, then starts to pull off the dinner-plate sized flowers and stuff them into his battered rucksack. Maybe on the next jaunt, he can find a bottle and some sugar. Make some dandelion wine.
The shift hits him between zipping his rucksack up and hefting it to his shoulder: he is now standing in the middle of a four-way intersection at rush hour. A yellow cab nearly runs him over: the man behind the wheel is shouting at him, waving a wide-fingered hand as his ruddy face roars, twisted in rage. His eyes are empty, and his passengers are only corpses.
He steps aside and looks up into a vermillion sky: the noonday sun is crimson, the color of blood. It is bloated, too large, taking up nearly half the sky, and the light is dim enough to gaze into, to see the wide, blotchy, diseased patches that dot the surface of that shining orb.

All we can do is place one person outside it. An Outside Observer, unaffected by the shifts. We drew straws. We chose you.

Twenty-one minutes. That was how long the world lasted. He hits the stopwatch, resets the counter.
There is a supermarket on the corner. The plate-glass window is shattered, and a man, now long dead, has been hurled through it. He steps over the glass and into the empty, deserted aisles. He is hungry. He is always hungry.
He ignores the rotting displays of fruit, buzzing with flies, or the greenish, molding displays of meat in the butcher's aisle, and heads straight for the canned goods. On the way, he passes by the dried goods. Something makes him pause. It's a box of instant stuffing. The front shows a typical Thanksgiving scene in the style of Norman Rockwell. The father is carving into a screaming human head. The apple-cheeked children are passing around plates of body parts.
He takes down a can from the shelf, a thin rectangular can in the style of a sardine tin, and opens it up with the twist key. Seventeen baby blue eyeballs packed in oil stare back up at him.
He grabs as many cans as possible. He can't afford to be picky.

We know what caused this, but it's too late. We can't stop it. Reality, as we know it, will vanish into the sea of chaos. Into the seafoam of the What-Could-Have-Been.

This time, the world lasts a full half-hour before the shift. He hits the stopwatch, resets the counter. The world is filled with fog. From out of the fog come men, or creatures very much like men. His machete is drawn before the first one reaches him, its broad mouth open impossibly wide, revealing a maw filled with jagged, sharklike teeth.

The nature of Reality is that of a multiverse. Choice causes new universes to branch out. Possibility creates new realities. Always before, however, those parallel universes have been separate, distinct. That is changing.

The next few minutes are difficult. He kills many, but they are legion. He is thrown to the ground. They tear open his pack like a bloated corpse and scatter the contents. They grab hold of the cans and slam them against rocks and broken bricks, bursting them open and devouring the eyes, fingers, and tongues within. Then they turn on him.

This is a visual representation of the CK-Class Restructuring, they told him. The spirals represent the universes. They are converging.

He is lucky. The world only lasts nine minutes, but that is long enough for one of the shark-faced creatures to take a bite out of his arm. He emerges into a new world. It is raining, and the rain is made of shit and blood.

When they woke him from his bed in the middle of the night, he knew it would be bad. But then, he had been ready. His years in the Army had taught him no fear, had taught him how to survive against all odds. He was ready to face whatever they needed him to face, kill whatever they needed him to kill.
He didn't expect that they would take him into a room and show him a movie: a false color representation of a mathematical reality. It looked beautiful: a sea of blue foam with bubbles forming and popping, with brilliant yellow spirals floating among them. The spirals, he noticed, were getting closer together, and their colors were fading.
It reminded him of back on the farm, in his childhood, when his grandfather used to make dandelion wine with the flowers his grandmother and sister would pick from the rolling green fields. The old man would put the flowers into a big pyrex cooking pot and fill it with water, some sugar, and lemon juice, and he would watch, spellbound, as the yellow flowers rose and fall in that boiling liquid, turning slowly in the bubbling water, changing color from bright yellow to dull brown.

He hits the stopwatch and resets the counter.