"Aren't the nights long now?"
Translation:Nejsou teď noci dlouhé?
The word order is strange and the ty is extraneous. Even without the ty it would be strange, although acceptable.
There are no specific nights to point to. If you were pointing to specific nights you would either be speaking in he past tense "Nebyly ty noci teď dlouhé?"
BUT I can imagine (not accepted yet) "Nejsou ty noci teď dlouhé?" quite well, though it might be colloquial, I am not sure.
Perhaps we will accept it in the future.
"Nejsou ty noci teď dlouhé?", which you just referenced, was my stab at this, so I just reported it in case the team wanted to take another look.
Of course, particularly here in the early modules, a lot of people will be grappling with the appropriate use of "ten" and its various forms. I can only really speak for myself here, but as one native English speaker, it does take a while to get comfortable avoiding leaning on "ten" as a replacement for a definite article. To my ear, important information is missing, as the article often conveys subtle distinctions (e.g., in English, "Aren't nights long now?" "Compared to when -- the summer, or the time of the dinosaurs?" "Aren't THE nights long now?" "Oh, yeah, THESE ones -- yeah, they're longer than a couple of months ago"). But, I realize Czech has gotten along without articles for hundreds of years...
Very strange. I can imagine it without "ty", though it would still be unusual, but hardly this way.
"Nejsou noci dlouhé teď?" strongly stresses TEĎ and means: The nights will be long in one month. Aren't the nights long NOW? Za měsíc budou noci dlouhé. Nejsou noci dlouhé teď?
The answer that is suggested to you can be any legal translation of the sentence. We have to accept all legal translations (even if their words or grammar weren't taught yet) and any accepted translation can be offered to you by Duolingo. There is no way out of this. The official translation above does not use "nyní" but "teď".
That could theoretically happen when you have some error in your sentence. But I can assure you that there is not a single accepted word order that would not accept "teď". All accept both "teď" and "nyní" (and some more). But if your answer is not accepted you can get various suggestions from the automatic Duolingo system. AFAIK the system does not look whether the words in the answer have been taught already.