The Shulhan Aruch (559) records a custom to bake the Massot for the Seder on Ereb Pesah after Hasot (Midday).The reason for baking in such a narrow timeframe is based on the analogy of Massa to the Korban Pesah. Just as the Pesah offering was brought after noon on Ereb Pesah, so too the Massot for the Misva of the Seder are also baked at that time.
The Tur (Rabbenu Yaakob Ben Asher, 1269-1343) and the Rosh (Rabbenu Asher Ben Yehiel, 1250-1327), record this as a mandatory practice. According to them, one does not fulfill the Misva of eating Massa with Massot baked at another time. However, Maran formulates this practice as a custom, not as a requirement. In fact, the Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933) and the Aruch Ha’shulhan (Rav Yechiel Michel Epstein of Nevarduk, 1829-1908) point out that most people do not observe this custom. It is too "risky" to bake Massot after noon on Ereb Pesah, since there are opinions that even a "Mashehu"-minute amount of Hametz is forbidden. It is too difficult for most people to safeguard against even a particle of Hametz. Therefore, the majority of Jews get their Massa before Ereb Pesah. The Vilna Gaon, Hazon Ish and the Brisker Rav did not follow this practice. On the other hand, Hacham Ovadia and Hacham Ben Sion would make a point to use Massot baked on Ereb Pesah for the Seder.
According to the Hida (Rav Haim Yosef David Azulai, 1724-1807) and Rav Haim Palachi (Turkey, 1788-1869), those who do bake Massot on Ereb Pesach, follow the order of the service in the Bet Hamikdash. They first pray Minha Gedola (Early Afternoon Service) corresponding to the "Tamid Shel Ben Ha’arbayim"-The daily afternoon offering-which was brought before the Korban Pesah. They then bake the Massot while reciting the Hallel, as was sung by the Leviim during the sacrifice.
SUMMARY
It is praiseworthy to use Massot baked on Ereb Pesah after Hasot for the Seder, if there is a reliable Hashgacha supervision.
