Translation:We have to be at the school by nine o'clock sharp.
But you don't have context. Duolingo lacks flexibility, and probably make sure you miss more than you would otherwise to try to take your hearts and get you to buy into the pay your way system. It can be very frustrating oh, but the best thing to do is to do as you're told, but recover your hearts by doing practice, which gives you experience points and hearts. Keep playing for free.
Yes, to me, Duolingo is trying to emphasize the importance of being there on time, I know this by the fact that Duolingo used "have to" and "9 o'clock sharp". The fact that they added the word, "sharp" (they must be there exactly by 9 o'clock. To me, means "be at the school" instead of the more casual, ""be at school". At least this is what I would say. Plus, dropping kids off at school must adhere to a strict time standard and be punctual, no matter what country you are in!
"sharp" is standard English. It emphasises that there will be no tolerance for being late (e.g. an appointment), or the event will start without you if you are late (e.g. a movie), as distinct from just being the time you are supposed to be there but they will wait for you if you are a bit late (e.g. meeting a friend). Of course if your friend is intolerant of tardiness he/she might use "sharp" after the time and that means you had better be there at the stated time or else!
It considers "at school" rather than "at the school" to be a typo (but accepted anyway). It's not a typo, though, both are reasonable.
Also, where does "have to be" come from? Isn't 要到 more like "will arrive", or perhaps (eh) "want to arrive"? I'd expect 得 or something, for "have to"
Both from what I've been told, and in my grammar (Modern Mandarin Chinese Grammar: A Practical Guide), 要 can be used for want, need, and future. How does one distinguish between "We want to be..."/"We need to be..."/"We will be..."? From experience, I'd guess it's like most things in Chinese: adding a second character (e.g. 想要，需要，等等) or context. Is this just a matter of collocation?
It depends on context (who's saying it, and their intentions), but "at" is a little less precise. "At" could refer to being within the school grounds (from a child's point of view, or a parent visiting on parent's evening), or could just be referring to being in the school's vicinity, such as at the school gates for a parent dropping off their child. Being "in" school - in the context of the statement in this exercise - more concretely refers to being within the school grounds (for whatever purpose).
Of course that would be clearer, e.g. if the requested sentence was: "We have to be IN CLASSS. Unfortunately Duolingo did not choose this ... The compilers of this course will not have foreseen that this sentence can be polyinterpretable. The use of 到 (dào) does not make it clearer either.
"sharp" is standard English. It emphasises that there will be no tolerance for being late (e.g. an appointment), or the event will start without you if you are late (e.g. a movie), as distinct from just being the time you are supposed to be there but they will wait for you if you are a bit late (e.g. meeting a friend).
Nobody has ever said, "by 9 o'clock sharp" to me in the United States my entire life. We might say, "at 9 o'clock sharp" meaning at precisely that time, not before or after. I think the Chinese character 整 means "by some time". If someone said ”九点整回。” and you came back at 8:45, I don't think it would be weird, but somebody who has lived in China might correct me.
First, no one says 'sharp' in ordinary English, and 几点整 is an ordinary way of saying 9:00 that doesn't connote excessive compulsion and precision. Second, DL is totally inconsistent with when they do or don't want 'sharp' so it's pure guesswork, not regarding meaning but regarding what the algorithm or whatever it is has decreed. Annoying!