"You read at night."
Translation:Vous lisez la nuit.
Well the sentence is not well translated in my opinion.
"Vous lisez dans la nuit" = "You read in the night"
"Vous lisez la nuit" = "You read at night"
As for your questions @danapplegate, I suppose you're asking if there is a possibility to translate "at night" with "à la nuit" to which the answer is no.
Maybe there are sentences using "à la nuit" but I can't think about any right now, and they would likely have no link with this exercise.
Searching for logical explanations is not always a good way to learn a new language, because all languages have different logic patterns, and most of them have exceptions. As a matter of fact, French has a tremendous amount of exceptions (which is part of the reason many people find it difficult to learn).
We usually don't use "à" when we talk about a whole portion of time (unless we use an expression that requires to use "à", for example "par rapport à").
"Le hibou dort le jour et chasse la nuit." = "The owl sleeps during the day and hunts at night."
However we use it for exact moments in time, for example:
"Il est arrivé à 15:00." = "He arrived at 3 o'clock."
You can learn more about "à" here: