Princess Celestia stood resting her hooves on the railing of her high balcony and watched as shadows from the setting sun rushed to overtake Canterlot. She didn't move as hoofsteps approached from behind and a pony cleared their throat.
“Princess,” said the hushed voice of her secretary, Raven. “You should get some rest. We must be up early for the Summer Sun Celebration.”
Celestia didn't turn. “Do you remember Sunset Shimmer?”
“...Indeed.”
“I know she was… troubled. But she had so much potential.”
“I know you’ve missed her.”
Celestia sighed. “So very much potential, Raven. The day ahead isn't one I’d hoped to face alone.”
“But Princess, you won't be. We’ll be together, in Ponyville.”
Celestia watched as the sun fell below the horizon. The stars nearest the mare-marked moon shone brightly.
“No,” she said. “Remain in Canterlot. If the sun is late in rising… have the mirror smashed. Immediately.”
This is how a one shot is written!
So, are you hinting that this is where Celestia was as Twilight and Starlight were bouncing around in time and relative dimensions in space??? And will you develop this in "To Serve in Hell?"