The Shulhan Aruch (687:1) records the Halacha that the Megila is read twice on Purim-once at night and once during the day. The Poskim discuss a case in which a person can only hear the Megila at only one of those times. Is it preferable for him to hear it in the night or during the day?
Hacham Ben Sion (Or L’Sion Vol. 4, p.319) suggests that this dilemma is a function of the Machloket between the Shulhan Aruch and the Rama regarding reciting the Beracha of Shehechiyanu on the daytime Megila reading. The Rama holds that even if one heard the Megila the previous night and recited Shehechiyanu, nevertheless, he recites the Beracha again before the morning reading. This ruling is based on the opinion of the Tosafot and the Rosh who hold that the primary Pirsum HaNes-publicizing of the miracle- is via the daytime reading. Therefore, Shehechiyanu is recited again during the day. Accordingly, if one can only hear the Megila once, it is preferable to wait until the daytime reading, which is the primary obligation.
On the other hand, the Shulhan Aruch rules that one does not recite Shehechiyanu prior to the daytime reading. Apparently, he holds that the daytime reading is equal in stature to the nighttime reading. Accordingly, one who can only hear the Megila once, should take advantage of the first opportunity to perform the misva, and hear it at night. This is the conclusion of Hacham Ben Sion, who cites the Aruch Ha’shulhan (Rav Yechiel Michel Epstein of Nevarduk, 1829-1908) who rules this way, as well.
The Shulhan Aruch also records the Halacha that one may interrupt Torah study in order to hear the Megila reading. This ruling is somewhat puzzling. Why is hearing the Megila considered an interruption of Torah study? Wouldn’t The Megila, one of the books of Tanach, also constitute Torah study? The Aruch Ha’shulhan answers that, in fact, the Megila is also Torah study. However, the Halacha is referring to a case in which a person is learning Torah in his home; in order to hear the Megila, he must make his way to a different location in order to hear the Megila with a Minyan. The traveling time, to and from the synagogue, is the interruption of study referred to as warranted in order to hear the Megila.
Hacham Ben Sion clarifies this Halacha and rules that Bitul Torah-interrupting Torah study- for Megila is warranted only when a person wants to join a larger gathering. The benefit of "B’Rov Am Hadrat Melech"- the praise of Hashem amplified in large gatherings- overrides the importance of Torah study. For example, if a Rabbi wants to give a class to a group before reading the Megila, and they do not intend to join a different, larger gathering, they may continue the shiur, since interrupting the study would not lead to a larger gathering.
Because of this principle of "B’Rov Am Hadrat Melech," the Sha’arei Sion (687:10), citing the Haye Adam, rules that even if a person has a minyan in his house all year long, he should disband his private Minyan and join the larger congregation for Megila reading. It is ironic that, unfortunately, nowadays, even people who pray in a large shul all year long, form their own Minyan for Megila on Purim. One should make an effort to join a major gathering for Megila reading, unless there are extenuating circumstances.
SUMMARY
1. If one can only hear the Megila read once, it is preferable to hear the night-time reading.
2. It is permitted to interrupt Torah study to hear the Megila only if the interruption will enable the person to hear the Megila read in a larger, public gathering.
3. One should not form private Minyanim for Megila reading.
