Issur to Eat before Maariv
Krias Shema
26. Starting a meal. One may not start eating a meal within half an [halachic (מ''ב סי' רל''ב סק''ז )] hour of the zman for the evening Krias Shema (שו''ע סי' רל''ה ס''ב ), i.e., tzeis (מ''ב סקי''ט ). This is because a person’s meal might drag out, leading him to forget to say Krias Shema. In Eretz Yisroel, where the Geonim’s tzeis is about twenty minutes after shekiya, one may already not start eating about ten minutes before shekiya.
27. Started. If one mistakenly started a meal after zman Krias Shema arrived or within half an hour of the zman, he must stop eating at tzeis; say Krias Shema, which is d’oraisa, without the brachos, which are d’rabanan; continue his meal; and daven Maariv with Birchos Krias Shema later (שו''ע סי' רל''ה ס''ב ).
28. Began permissibly. If one began permissibly, i.e., more than half an hour before, he does not need to stop as long as he has time to say Krias Shema after his meal (מ''ב שם סקכ''א ).
Maariv
29. Starting. For Maariv as well, one should l’chatchila not start eating a meal within half an hour of tzeis – neither a big meal, e.g., a wedding meal, nor a small meal, e.g., supper at home or a Shabbos seuda (מ''ב סקט''ז ).
30. Started. If one started a meal within this time, he does not need to stop eating to daven as long as there is time to daven afterward, as tefilla is d’rabanan (שו''ע ומ''ב שם ).
Small Amount
31. One may eat a small amount of food [טעימה] even after the zman for the evening Shema arrives. The permissible amount is: up to a k’beitza of bread (מ''ב שם סקט''ז ); up to a k’beitza of pas haba’a b’kisnin (שעה''צ סי' רפ''ו סק''ז, מ''ב סי' תרל''ט סקט''ז ); even a larger amount of cooked mezonos without making it into a proper meal [קביעות סעודה]; and even a large amount of fruit or sweets (מ''ב סי' רל''ב סקל''ד ). One may also drink a lot, as long as it is not intoxicating drink (מ''ב שם סקל''ה ).
Appointing a Shomer
32. If one appoints a person of at least bar mitzva age (ערוה''ש סי' ער''ה ס''י ) who is not eating at the meal to remind him to daven after the meal, he may begin eating even if the zman to daven has arrived (מ''ב סי' רל''ה סקי''ז ). Also, if one began when he shouldn’t have but then appoints a shomer, he may continue his meal (הגר''ח קנייבסקי, אשי ישראל פכ''ז הע' ס''א ).
33. If multiple people have not davened and are sitting down to eat a small meal, each one can appoint another one as a shomer, because when there are lots of people, they will remind each other (מ''ב בהקדמה לסי' תרס''ט, א''א בוטשאטש סוף סי' רל''ב ).
34. Phone as shomer. One may set an alarm clock, e.g., on his phone, as a reminder to daven; that has the status of a shomer. But when he hears it ring, he must stop right away and daven, not postpone the alarm for later (הגרשז''א, שבות יצחק ח''ב פכ''ג אות ג').
35. Set minyan. The poskim say that if a person has a set minyan for Maariv that is generally part of his daily schedule, he may be meikel to eat beforehand, relying on the fact that he will follow his routine and not forget to daven. The fixed time is like his shomer (ע''פ ערוה''ש סקט''ז, שעה''צ סקי''ט, שו''ת אג''מ ח''ד סי' צ''ט, שש'כ פנ''ו הע' י''ב בשם הגרשז''א ).
36. Similarly, even if one does not have a specific set minyan, but he knows that he always goes to daven at a shtieblach at a particular time, e.g., he davens Maariv there after night seder, he may be meikel, relying on the fact that he will not forget and deviate from his daily schedule (פוסקים ).
