"No son minutos, sino horas."
Translation:It is not minutes, but hours.
Try to not to think too literally about translation. In english we do not say "they are not minutes" we say "it's not minutes". In spanish they happen to say "they are not minutes instead. There are many cases where a plural in English is a singular in Spanish also, "la gente es" and "the people are" being a famous one.
No, but you should not interpret the meaning of the sentence, but rather the translation. If you know what I mean? For example: If you se the sentence: "Mi madre" - everybody knows that it means "My mom", except that it doesn't, it means "My mother" - even though it might be the same thing, it is not. Same everywhere here on duolingo, you should translate the sentences correctly and not how you would interpret it, as these are two completely different things.
Because in English you do not say "they are minutes". It's actually strange of English we don't make the pronoun plural when the noun is in this case. Spanish is more "correct" as they do. Language is not an exact science and you have to expect these sort of discrepancies when translating. To be honest it's amazing there are so few.