It is forbidden to start eating, even a light meal, half an hour before tzeit hakochavim, for perhaps one will continue his meal until he becomes tired and falls asleep. It is also forbidden to drink alcoholic beverages. However, fruits and vegetables may be eaten. Even the consumption of bread or grains in an amount less than a kabeitzah is permissible. If a person began eating before half an hour prior to tzeit hakochavim, since he started to eat when he was permitted to do so, he may continue, provided that he will have enough time after his meal to recite Shema and pray (Mishnah Berurah 235:21).
If a person began to eat when it was forbidden to do so, he must stop his meal in order to recite Shema, which is a biblical commandment. However, with regard to Birkot Keriat Shema and the Amidah, since they are rabbinic mitzvot, he is permitted to delay their recital until after he finishes eating (Shulchan Aruch 235:2).
If he asks a friend who is not eating to remind him afterwards to recite Shema and recite the Amidah, he is permitted to begin eating even after tzeit hakochavim in times of need (Mishnah Berurah 235:18). If two people need to eat and did not yet pray Ma’ariv, in times of need they may make an agreement between themselves that they will remind each other to pray Ma’ariv, and in that way, there is no concern that they will forget (see Mishnah Berurah in the introduction of section 669). Likewise, a person who always prays in a certain minyan at a particular time, and knows that he will not forget to pray because the consistency of the minyan serves as his reminder, is permitted in extenuating circumstances to eat before Ma’ariv (see Aruch HaShulchan 232:16).
In many yeshivot in the summer, dinner is started within the half-hour before tzeit hakochavim, and they rely on the fact that the time of prayer is set and known to all, and that everyone reminds each other to pray Ma’ariv after the meal. Although l’chatchilah it is proper to pray before dinner, nevertheless, it is correct to practice the way many yeshivot do in order to preserve the order of the learning sessions. If the meal is delayed until after praying Ma’ariv, the afternoon learning session will be too long and the evening learning too short, and it will likely cause neglect of Torah study.
One who must eat before praying and has neither a permanent time to pray nor someone to remind him, may create a reminder to pray. For example, he can set an alarm clock to ring, or he can ask his friend to call him and remind him to pray, and the minute he hears the ring or his friend’s call, he must recite Shema and pray (Halichot Shlomo 2:12). B’dieved, he can tie something to his clothing, so that he cannot take off his clothes before going to sleep without noticing the reminder to recite Shema and pray.
Similarly, it is forbidden to sleep a regular sleep starting half an hour before tzeit hakochavim. In extenuating circumstances, in the beginning of the evening, when everyone is normally still awake, a person may go to sleep after appointing someone to wake him up before the time to pray (see Aruch HaShulchan 232:17).
A person who intends to pray Ma’ariv individually may not begin learning after tzeit hakochavim without praying first. However, before tzeit hakochavim, he may start learning even if he intends to continue learning through tzeit hakochavim. If he is accustomed to going to pray in a synagogue in a particular minyan that begins later, he is permitted to start learning in his house after tzeit hakochavim for there is no concern that he will forget his regular schedule (Shulchan Aruch 89:5; Mishnah Berurah 89:30-31; 235:17).
Some say that all activities prohibited by the Chachamim before Minchah are also forbidden before Ma’ariv, such as a task that will likely last a long time (Rashba; Mishnah Berurah 235:17). Others say that the Chachamim only prohibited starting those types of work before Minchah, because a person is used to working in the afternoon and can get so involved in what he is doing that he will forget to pray. However, in the evening, people do not usually get caught up in their work (Aruch HaShulchan 235:16, as implied from the Rambam and other Rishonim). L’chatchilah, in a situation in which there is concern that he will be tempted to continue working, it is proper to act stringently (see earlier in this book 24:5).