It looks like a plural, but in this case it is not. It's oblique. When a noun is followed by a post-position (में) it changes to the oblique case. घंटा is a singular masculine noun ending in आ, so it's ending changes to ए. Other singular nouns don't change. Masculine plural nouns get an ओं ending when followed by a post-position, and feminine nouns get an इयों ending.
I can't help you with a French or Spanish example. But, here is a simple explanation in English. http://www.learning-hindi.com/post/1116750602/lesson-48-nouns-in-the-oblique-case
Both those translations are very awkward one for English... and would not be used. The meaning is there and clear enough, but just not the way English speakers would say it. The Hindi literally is "In one hour how many minutes are there?" ... and so in English this is OK plus "How many minutes are there in one hour?" . Also the word "an" instead of "one" is OK in English (means the same.. but the literal translation from Hindi "eck" is of course "one"
Actually, in English, neither of these are awkward at all. I would say both of these, which is why I ask. It is not typically a question that an adult would ask, unless one was instructing someone who is learning to tell time, or by a child who does not yet know. In both cases, either of the translations I used would be just as easily spoken. And as to being awkward, it is difficult to ascertain how awkward something might sound while we are in the process of learning a language; we, for example, are routinely given sentences like, "Grandmother is sitting on the road", or "Cows are not cats" (won't the people of India think I am smart!). I am not trying to be argumentative; I am trying to learn nuance and how to discern word and sentence usage.
"harsh" is rather harsh, don't you think? It's not like Duolingo is fining us for incorrect answers. It's just a computer and at this point the Artificial Intelligence (AI) is completely unable to recognize a translation that misses the thought or concept expressed in the original language from a translation that is just awkward or lacking in artistry or atypical, but correct in a technical sense. AI is far, far from the ability to provide the nuance that a human teacher provides, but is also far, far less expensive.