PREPOSITIONS GIVE AWAY AMERICAN SPANISH
In an earlier post I mentioned the usage of "aquí" and "acá", in European Spanish vs American Spanish. This summer a colleague of my daughter's, Violeta, originally from Perú, in a café terrace in Madrid, was bantering about "por la mañana" and "en la mañana". She kept correcting herself, pointing out the difference in the usage of the preposition. This is another giveaway as to where the speaker hails from. "En la noche oigo ruidos raros" will tell you the speaker is not from Spain because she would have said: "Por la noche oigo ruidos raros." Is this important? Only if you use either preposition and a "native", a local, corrects you. Do not argue. Never argue about questions grammatical with average native speaker.