Incorrect answer

Question

"Nous avons mangé en une heure" does not have a correct answer.  "We ate in an hour" and "We ate in an hour´s time" are both incorrect.  An appropriate answer would be "We ate for an hour."  (American English)

Anne Davies · Accepted Answer

No expert, but my understanding of "en" is that it expresses the time frame within which something happens, the time it took - we weren’t necessarily eating for the whole hour. "In an hour" seems a good rendering (UK English) of "en une heure" for events in the past. Whereas "dans une heure" is looking forward to a future event and can usually translate as "in an hour’s time" as well as "in an hour".
 
However I do find "within an hour" is used confusingly in this lesson and discussion, as "within" implies to me the time by which something happens (="d’ici une heure").

Maarten Kamp · Answer

To add to Anne’s response,
The question noted is a copy of one of the examples in the lesson, with only a change from 40 minutes to 1 hour. 
The lesson example is translated to ‘ We ate in 40 minutes ‘. Not as precise as it could be, but standard everyday English, at least in some parts of the English-speaking world. 
This translation to English reflects the original French meaning of ‘ nous avons mangé en 40 minutes ‘  - a sentence which does not necessarily imply eating (constantly) for 40 minutes.
‘ Nous avons mangé (pendant) 40 minutes ‘ would be ‘ we ate for 40 minutes ‘.
 https://progress.lawlessfrench.com/revision/grammar/expressing-for-duration-with-either-pendant-durant-depuis-or-pour