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Hi Antonio. To aid to route name-free interaction utterances to your skills, it’s recommended to implement CanFulfillIntentRequest (CFIR), although it is optional. The implementation of CFIR is useful in cases where the ability needs to reject a request (via "NO" as a response) dynamically at runtime to provide a better client experience.

For more info, please have a look at the guidelines and FAQs in our documentation here:
Guidelines: https://developer.amazon.com/ja-JP/docs/alexa/custom-skills/understand-name-free-interaction-for-custom-skills.html#dos-and-donts-for-optimizing-your-interaction-model-for-nfi
FAQs: https://developer.amazon.com/en-US/alexa/alexa-skills-kit/get-deeper/engagement-tools/nfi-toolkit-preview.html

Regarding the expected time and according to the point 5 of the following documentation, with the recurring training of Alexa machine learning and artificial intelligence, it might take up to eight weeks for Alexa to route name-free interaction utterances to your skills.
https://developer.amazon.com/ja-JP/docs/alexa/custom-skills/understand-name-free-interaction-for-custom-skills.html#using-the-nfi-toolkit-in-preview