@rintagea  
Trolluna.

I imagine them sitting together the next day.
 
“So… when are you gonna turn into Daybreaker?”  
“Luna I already apologized.”  
“I just wanna be ready for when it happens. Just tell me if you feel like taking control, I’ll grab twilight and her little friends and you can go to the sun for a bit to cool off.”  
“I don’t want to take full control over equestria.”  
“I’m just saying, the sun is always nice this time of year.”  
“You’re never gonna let me live this down are you?”  
“Nope.”

@Ryodraco  
She will forgive her sister (but there will be no cake for one week).

I wonder what Celestia may have to do to make this up to her, or if Luna will just let the issue slide with perhaps a sarcastic remark later on.

Wow, good job storyboardists/animators. A big piece of character development is consistency and that is exactly the face Luna would make if her night was abruptly ended by Celestia for entertainment.

luna : Tia what are you doing with my night.

“Aaaaaand there goes my sister raising the sun several hours before before she’s supposed to. You attention hog.”

@Xonxt  
There was no other way out at this time.

“So we won’t frivolously raise our celestial bodies for Twilight’s nation-wide celebration in the movie, but this is perfectly fine?”