Beginning at chatzot, a person must be careful not to forget to pray Minchah; therefore, he may not start a large feast before reciting Minchah. A large feast is one in which many people partake, such as meals which accompany a brit milah, sheva berachot, and a pidyon haben. However, a Shabbat meal is not considered a large feast. In extenuating circumstances, it is permitted to begin a large feast before praying Minchah, on condition that it is clear to those who are eating that they will surely end the feast before the time to pray Minchah lapses, and that they will remind one another to pray after the meal.
Starting from half an hour before Minchah Ketanah, approximately three hours before sunset, a person must not begin eating even a small meal before he recites Minchah. However, if there is someone there to remind him to pray Minchah, he is permitted to eat. In a place in which he does not have someone to remind him, it is also possible to set an alarm clock to ring at the time that he must pray Minchah. Yet, he must be sure that immediately upon hearing the ring, he will stop his meal and go pray (Rama 232:2; Bei’ur Halachah “V’Yesh”; Halichot Shlomo 2:12).
Once chatzot arrives, some try, l’chatchilah, not to eat even a small meal before reciting Minchah. Therefore, in many yeshivot, Minchah is held early in the afternoon so that after they pray, they can eat lunch according to all opinions.
. This is based on the Rif and the Rambam, as clarified in note 6. Although the Shulchan Aruch 232:2 rules like them, still, Sephardim are accustomed to acting leniently, see Kaf HaChaim 30, Yalkut Yosef, part 3, 232:8. However, l’chatchilah it is good to be stringent and pray before the meal, as explained in Or L’Tzion, part 2, 15:1-2 and Yechaveh Da’at 4:19.
In extenuating circumstances, it is possible to be lenient and eat a regular meal, even within the three (proportional) hours close to sunset, even when he does not have someone to remind him to pray or an alarm clock to set. This is on condition that he regularly prays in a set minyan, as maintained by Aruch HaShulchan 232:16. This is also the opinion of the Mahariv, as brought by the Mishnah Berurah 232:26.