The Shulhan Aruch (Orah Haim 238:1) codifies the obligation to spend some time learning Torah every night, emphasizing that the importance of nighttime Torah learning exceeds that of daytime learning. He goes so far as to warn that if one does not learn Torah at night, "his punishment is very severe."
The Mishna Berura (commentary by Rav Yisrael Meir Kagan, 1839-1933) explains this Halacha based upon the Sages’ comment that "nighttime was created specifically for learning." Since the period of night – when people do not generally work – is intended primarily as a time for Torah study, one must ensure to use the nighttime hours for this purpose. The Mishna Berura then proceeds to cite a number of different comments from Hazal regarding the reward for learning at night, and, Heaven forbid, the punishment for neglecting this obligation. Thus, for example, the Sages state that if somebody learns Torah at night, "the Almighty stretches a thread of kindness over him during the day." The Sages also establish that a person who learns Torah at night is considered as having offered sacrifices in the Mikdash, and that such a person is rewarded by having the Divine Presence in front of him at all times.
The Mishna Berura also cites in this context the comment of the Rambam (Rabbi Moshe Maimonides, Spain-Egypt, 1135-1204), in Hilchot Talmud Torah (3:13), that "one who wishes to merit the crown of Torah" must ensure not to waste even a single night indulging in excessive sleep, eating and the like. As the Mishna Berura notes, the Rambam’s comments imply that even during the summer months, when the nights are short, one must ensure to spend time learning Torah and not waste the whole night sleeping or engaging in other activities. In fact, he adds, the Sages warn that a house in which Torah is not studied at night will be "consumed by fire." The Mishna Berura also draws our attention to the Sages’ comment that when Torah scholars indulge in sleep at night instead of learning Torah, "it is bad for them and it is bad for the world."
The Magen Abraham (Rabbi Abraham Gombiner, Poland, 1637-1683), commenting on this Halacha, writes that the Sages did not specify a particular amount of time that one must spend learning at nighttime. This therefore depends on each person’s physical condition and ability; everyone must spend as much time studying Torah at night as he can.
In the next Halacha, the Shulhan Aruch rules that if a person has a regular, scheduled regimen of learning each day, and one day he cannot, for whatever reason, learn his daily quota, he should ensure to make it up that night. Even if the night is short, he emphasizes, the person should not go to sleep until he completes his quota, rather than delaying the study until the next day. Accepting upon oneself a specific schedule of learning amounts to a Neder (vow), which one is bound to fulfill. Therefore, a person who fails to fulfill this commitment one day must do so immediately that night, rather than wait until the next day, when he will already be required to learn that day’s quota.
Summary: One is obligated to some spend time learning Torah every night, as much as he can. A person who has a fixed, daily quota of learning must ensure to complete the quota, and if he misses a day, he should make it up at night, rather than wait until the next day.
