Until what time in the day is considered ‘pas shacharis’?
The Gemara (Bava Metzia 107b) prasies its virtues, yet does not set a time until which eating a meal would constitute pas shacharis. It would appear that the meaning is the breakfast meal, and it can be eaten at whatever time it is normal to eat breakfast. The time for breakfast can vary considerably according to society, but all societies have a “morning meal,” and this is the meal that the Talmud is referring to. According to this definition, there is room to inquire as to whether today’s “brunch,” which merges breakfast and lunch as a mid-morning meal, would constitute pas shacharis.
Yet, it should be noted that Maseches Derech Eretz Rabbah (chap. 7) writes that one should not eat until the fourth hour of the day, and Maseches Kallah Rabasi (chap. 10), states that this refers to a major meal, but pas shacharis can (and should) be eaten before this time. This implies that the time for pas shacharis is until the fourth hour of the day. See also Shulchan Aruch (Orach Chaim 155) and Mishnah Berurah, which state that a person should eat a small amount before going to study, and this would apparently be considered the pas shacharis.
Based perhaps on Shulchan Aruch 157:1, Mishnah Halachos (vol. 7, no. 25) writes that the time for pas shacharis extends until the sixth hour of the day.