The fuquhaa agree that zakaat ul-fitr is due at the end of Ramadhaan. They differ, however, about the exact time.
Ath-Thawree, Ahmad, Ishaaq, and ash-Shaafi’ee (in his later opinion) and Maalik (in one of his reports) are of the opinion that it is due at the sunset of the night of breaking the fast, for this is when the fast of Ramadhaan ends. Abu Hanifah, al-Layth, ash-Shaafi’ee (in his earlier opinion) and the second report of Maalik say that zakaat ul-fitr is due at the start of fajr on the day of ‘eed.
These two different views acquire relevance if a child is born after sunset but before dawn on the day of the ‘eed; the question then is whether zakaat ul-fitr is due on the child or not. In accordance with the first view, it is not since the birth took place after the prescribed time, while according to the second view, it is due because the birth took place within the prescribed space of time.
From Sayyid Saabiq’s Fiqh us-Sunnah
With commentary by Muhammad Naasir ad-Deen al-Albaanee from Tamaam ul-Minnah fit-Ta‘leeq ‘alaa Fiqh as-Sunnah