Mishneh Torah (Rambam) משנה תורה

The mitzvah of reciting the Morning Prayer entails that one begin praying at sunrise. The time [for prayer, however,] extends until the fourth hour, i.e., a third of the day. If one transgresses or errs and prays after the fourth hour, he has fulfilled the obligation of prayer, but not the obligation of prayer in its time. Just as prayer is a positive Scriptural commandment, so too, its recitation at the proper time is a Rabbinic commandment, as established for us by Sages and Prophets.

We have already stated that the time of the Minchah Prayer was established in correspondence to the daily afternoon sacrifice. Since the daily [afternoon] sacrifice was offered every day at nine and a half hours, [the Sages] established its time as nine and a half hours. This is referred to as "the lesser Minchah." When the eve of Pesach fell on Friday, they would slaughter the daily [afternoon] sacrifice at six and a half hours. Accordingly, [the Sages] ordained that one who prays [Minchah] after six and a half hours has fulfilled his obligation. When this time arrives, the time of its obligation begins. This is referred to as "the greater Minchah."

Many people are accustomed to recite [the afternoon service at both Minchah] Gedolah and K'tanah, and [to consider] one of them as an optional prayer. Some of the Geonim taught that it is proper to recite the optional prayer only [at the time of Minchah] Gedolah. This is reasonable, since it corresponds to [the offering of a sacrifice] which was not frequent every day. If one recites [the service] as an obligatory prayer [at the time of Minchah] Gedolah, he should recite it only as an optional prayer [at the time of Minchah] K'tanah.

Behold, you have learned that the time of Minchah Gedolah is from six and a half hours until nine and a half hours, and the time of Minchah K'tanah is from nine and a half hours until there are one and a quarter hours left in the day. One may [however,] recite [the afternoon service] until sunset.

The proper time of the Musaf Prayer is after the Morning Prayer, until seven hours of the day. One who recites it after seven hours, even though he has acted negligently, fulfills his obligation, since its time is the entire day.

Regarding the Evening Prayer - even though it is not obligatory - a person who does recite it [must know that] its proper time is from the beginning of the night until dawn. The proper time of the Ne'ilah prayer is such that one completes it close to sunset.

One who recites a prayer before its proper time does not fulfill his obligation and must recite it again at its time. If, due to extenuating circumstances, one recites the Morning Prayer after dawn, [but before the proper time], he does fulfill his obligation. One may recite the Evening Prayer of the Sabbath night on the eve of the Sabbath before sunset. Similarly, he may recite the Evening Prayer of Saturday night on the Sabbath. Since the Evening Prayer is not obligatory, we are not especially careful about its time. Nevertheless, one must recite the Shema at its proper time after the appearance of the stars.

Anyone who intentionally allowed the proper time for prayer to pass without praying, cannot rectify the situation and cannot compensate [for his failure to pray]. [If he unintentionally failed to pray or was unavoidably detained or distracted, he can compensate for the [missed] prayer during the time of the prayer closest to it. He should first recite the prayer of this time, and afterwards, the [prayer of] compensation.

How is this [exemplified]? One who errs and does not recite the Morning Prayer before half the day passes should recite the Minchah Prayer twice, the first as Minchah [itself] and the second as compensation for the Morning Prayer. One who errs and does not recite the Minchah Prayer before sunset should recite the Evening Prayer twice, the first as the Evening Prayer [itself] and the second as compensation for the Minchah Prayer. [Similarly,] one who errs and does not recite the Evening Prayer before dawn should recite the Morning Prayer twice, the first as the Morning Prayer [itself] and the second as compensation for the Evening Prayer.

One who errs and does not recite two consecutive prayers can only compensate for the last of them. How is this [exemplified]? One who errs and recites neither the Morning Prayer nor the Minchah Prayer should recite the Evening Prayer twice, the first as the Evening Prayer [itself] and the last as compensation for Minchah. The Morning Prayer, however, has no compensation, since its time has already passed. This is also the case for other prayers.

If two prayers are before him, Minchah and Musaf, he should first recite Minchah and afterwards Musaf. There are those who teach that one should not do this in a congregation, in order that people not err.