ANSWER: You can intend voluntary fast any time providing you didn’t consume anything after Fajr. 

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No. Kindly refer to the following link(s): https://m.youtube.com/watch?v=20vzfCswEAs

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If you didn’t fast because of menses it is sufficient to make your fast. If you didn’t fast due to illness, and you have chronic disease, you  have to give kaffara for one meal.

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