You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
American_Broadcasting_Company

Context:
On May 1, 1953, ABC's New York City flagship stations – WJZ, WJZ-FM and WJZ-TV – changed their respective callsigns to WABC, WABC-FM and WABC-TV, and moved their operations to facilities at 7 West 66th Street, one block away from Central Park. The WABC call letters were previously used by the flagship station of CBS Radio (now WCBS (AM)) until 1946. The WJZ calls would later be reassigned to the then-ABC affiliate in Baltimore in 1959, in an historical nod to the fact that WJZ was originally established by the Baltimore station's owner at the time, Westinghouse.

Question:
When did ABC's New York flagship stations change their call signs?

May 1, 1953