In one short story in ...y no se lo tragó la tierra by Tomás Rivera, a weird grammatical construction stuck out to me:
El fulano vino como a las dos semanas en una camioneta y con una trailer.
The English translation included in the book is:
A man came about two weeks later in a station wagon hauling a trailer.
And again, several sentences later:
A la semana se fueron sin decir una palabra.
A week later they left without saying a word.
This struck me as odd as I would have expected "a la semana siguiente".
Other common expressions for "a week later" I've seen are "una semana más tarde" or "una semana después". Most examples of "a la semana" I've seen have to do with rates, like "tres veces a la semana".
Is this a regional thing among migrant farm workers and/or in northern Mexico, or is it generally idiomatic Spanish?