It's midnight. The birthday for Zecora is over, the birthday for Cheerilee is about to begin.
We learn in 'A Friend in Deed' that Zecora's and Cheerilee's birthdays are only a day apart. I just think it would be fun if the two combined their birthdays into a two day celebration.
This is a psuedo-continuation of this: [link]
MLP:FiM belongs to LF and Hasbro