"What time is it?"
Translation:Τι ώρα είναι;
χρόνος is the concept of time (Time flies),ώρα is the specific hour . This question asks for the specific hour.
The exercise is to translate 'what time is it?'. So in Greek one asks for the hour instead of the time?
When you ask τι ώρα είναι you ask for the specific time -Τι ώρα είναι? -Είναι 8.30. Χρόνος is the concept of time.
The hints work as a dictionary. We do have to include all possible translations, but that doesn't mean that every single translation is appropriate and makes sense in a certain sentence. In this case, χρόνος wouldn't make sense in that context as a translation. ^.^ It would be correct, in sentences like
I don't have time - Δεν έχω χρόνο
Don't waste your time - Μην σπαταλάς τον χρόνο σου