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:
Daylight_saving_time

Context:
Some clock-shift problems could be avoided by adjusting clocks continuously or at least more gradually—for example, Willett at first suggested weekly 20-minute transitions—but this would add complexity and has never been implemented.

Question:
Willett's first suggestion was to change clocks by 20 minutes how often?

weekly