"Four weeks in February" is a literal translation, but it lacks a clear meaning in English. It sounds more like a description of a period of time, like Семнадцать мгновений весны.
"When will your vacation be?" "Four weeks in February."
"There are" is required to create the same meaning as in the Russian sentence.
I thought that at first, too, but then I remembered the "There is" skill, and how it puts what the subject is in or on at the front of the sentence ("в коробке мяч"). If you think of it that way, then you just consider a month being something that can have something in it, it makes sense.