"Micul dejun este dimineața."
Translation:The breakfast is in the morning.
No, when referring to a certain part of the day, you just use the word without "în". Examples:
Dimineața mă duc la școală.
După-amiaza beau un ceai.
Seara mă duc la cursul de limba română.
All these sentences imply the fact that this usually happens (a.k.a a schedule).
It means "the breakfast". Breakfast would be "mic dejun".
The sentence we are referring to here is correct in Romanian, however the translation is inaccurate, it should have been "Breakfast is in the morning". There are a lot of cases when you would use an article in Romanian, but not in the English translation and vice-versa. It's kind of a finesse thing which you learn with time and experience.