Twilight flung the door to the basement lab open and ran down the stairwell, muttering to herself. “I must go back before it’s too late. Every second counts!”

Her horn glowed and she scooped the miscellaneous experiments littering the floor with her magic, throwing them into a corner. She paid no attention to the sound of breaking glass and searched frantically around the room until her eyes landed on a piece of chalk. “Aha!” She grabbed it with her magic and started drawing an elaborate rune circle on the newly vacated floor.

“Come on, come on!” grumbled Twilight, throwing an occasional glance at the clock.

It was taking her longer than she expected to draw up the circle, which meant she had to amend her calculations on the fly. Several times, she had to erase portions of the circle and redraw them again with almost imperceptible changes.

Finally, it was complete.

Stepping inside, she stared at the clock. Three minutes had passed. The incantation was going to take exactly 36 seconds and a half. She could make it!

Twilight closed her eyes and started channeling magical energy with her horn. It flowed within her body, down her legs and into the rune circle beneath. She weaved the flow of arcane energy, tracing the outlines of the circle in her mind. With each molding of the stream, a corresponding rune turned from gray chalk to a live magical conduit, bright with the purple aura of its caster. 

Tendrils of magic rose from the circle. They swirling lazily at first, but with each passing second their brightness increased. The raw magical energy began tugging at Twilight’s hair, tossing it into disarray. The swirl of arcana flowed faster and faster, picking up paper notes into a roaring tornado with Twilight in its center.

At exactly thirty seconds since had begun casting, Twilight felt her hooves lift off the floor. She opened her eyes and blinding light streamed from them. The arcane energies reached their crescendo, tendrils of magic spiraling in all directions from the floating alicorn.
Then, reality imploded on itself.

[hr]

Twilight blinked. 

Before her stood an endless corridor made of light of every color and uncolor. In the corridor, an infinite number of Twilights blinked, mimicking her in a wave through time itself. She turned back and saw herself infinite in the other direction, the motion finishing with her and beginning at the edge of her perception.

She took a step back, merging into the Twilight behind her, who then merged into the Twilight behind that Twilight. Step by step, she counted aloud, and heard herself both from behind and in front, as each sound seemed to rise from behind her and die down somewhere in the infinity in front. She continued backing and counting. One count for each step. One merge. One moment in time, reversed.

The concept of time didn’t really exist once you are outside it, Twilight mused. All there is is moments. So, she counted them, and even though it felt like an eternity passed, it never really did.

She knew the number. Knew the moment she needed to return to. And it both never came and had always been there. Twilight recognized it.

For a moment, she stood still in time. Then, the corridor started to collapse around her, the infinity merging back into a singularity, and then Twilight blinked.

[hr]

Spike stood before her, scroll in hand, head drawn back and chest puffed with air.

“Waaaait!” Twilight shouted.

Spike startled and belched a blaze at the ceiling, missing the scroll.

“What gives?” he groaned as Twilight snatched the scroll from his claws.

“Wrong scroll!” Twilight said, hiding it behind her back. “I told you to send the one in the right drawer, not the left one.”

Spike scratched his head. “You sure? I’m pretty sure you pointed to the left one.”

“Spike!”

“All right, all right, sheesh,” Spike rolled his eyes and moved towards the desk. “Next time be more speci-” he couldn’t finish the thought as a belch echoed in the room and a scroll wearing the Canterlot crest appeared.

“Never a calm moment,” grumbled Spike before clearing his throat and reading.

“My Dearest Twilight, 

“I am happy to see the advancements you have made in temporal magic. Indeed, I’m sure your discoveries will imbue the field with renewed vigor and excitement.

“That said, I must urge you to choose the reason for time travel more carefully in the future. Temporal magic is a dangerous and powerful tool, not to be wielded frivolously by those who have control over it. I trust upon reflection you will agree that the current use was not really warranted, as there were a lot more conventional approaches one might have taken.

“That is to say nothing of the fact that I, being an alicorn as well, am also a part of the stream and sensitive to its changes. My memories of the… Mistake that occurred are fully present, making this whole ordeal not only dangerous, but also moot.

“I trust that this will be a learning experience for you.”

Spike scratched his head. “What was this about?”
  
Twilight was staring blankly forward, eyes turned to pinpricks, a deep blush across her face.

“Wait, there is something at the end,” Spike continued.

“PS. For what it’s worth, I found your poem delightful and I would very much love to be your little marshmallow. 
"XOXO, Celestia.”

Twilight collapsed in a heap, threw her hooves over her head and screamed.