The Sages taught:
The main mitzva of confession is on Yom Kippur eve when darkness falls. But the Sages said: "One should confess on Yom Kippur eve before he eats and drinkslest he become confused at the meal. And although one confessed before he ate and drank, he confesses again after he eats and drinks, as perhaps he committed some sin during the meal. And although one confessed during the evening prayer on the night of Yom Kippur, he should confess again during the morning prayer. Likewise, although one confessed during the morning prayer, he should still confess during the additional prayer. Similarly, although one confessed during the additional prayer, he should also confess during the afternoon prayer; and although one confessed during the afternoon prayer, he should confess again during the closing prayer [ne’ila]."

“It is an obligation to confess on the eve of the Day of Atonement when it gets dark, before he immerses himself in eating and drinking. Even though he confessed in the evening, he has to confess in the morning; though he confessed in the morning, he has to confess at musaf; though he confessed at musaf, he has to confess in the afternoon; though he confessed in the afternoon, he has to confess at neˋilah, for the entire day is qualified for confession.”

"Lest his mind be confused" - On account of drunkenness.

"A matter of corruption" – that is, of sin.

(7) Yom Kippur is the time of Teshuvah for all, both individuals and the community at large. It is the apex of forgiveness and pardon for Israel. Accordingly, everyone is obligated to repent and confess on Yom Kippur. The mitzvah of the confession of Yom Kippur begins on the day's eve, before one eats [the final meal], lest one choke to death in the meal before confessing. Although a person confessed before eating, he should confess again in the evening service, Yom Kippur night, and similarly, repeat the confession in the morning, Musaf, afternoon, and Ne'ilah services. At which point [in the service] should one confess? An individual confesses after the Amidah and the Chazan confesses in the midst of the Amidah, in the fourth blessing.

The Rabbis taught: The mitzvah of confession (vidui) is on the eve of Yom Kippur, toward nightfall. But the Sages said: One should confess before he eats and drinks, lest his mind become confused during the meal. And even though he confessed before eating and drinking, he must confess again after he has eaten and drunk, etc. It seems, from the precise wording, that the confession after eating is not the one recited in the evening (Ma’ariv) prayer, for it did not state: “Even though he confessed before eating and drinking, he confesses at Ma’ariv,” as it later states: “Even though he confessed at Ma’ariv.” Moreover, the teaching states that the mitzvah of confession on the eve of Yom Kippur is “toward nightfall,” i.e., after he has eaten and drunk. The Sages only required him to confess before eating because his mind might be disturbed during the meal. Therefore, it says that although they required him to confess earlier, he has not lost the proper time of confession and must confess again after eating and drinking—namely, at nightfall. But Ma’ariv is not called “after eating and drinking,” for it is not immediately following the meal; it is simply the evening prayer. Furthermore, what is meant by “even though”? Could it enter your mind that one would not confess on Yom Kippur itself? The confession of Ma’ariv is only in case some sin occurred during the meal. The mitzvah of confession on the eve of Yom Kippur, however, is with nightfall, while the confession of Yom Kippur itself is certainly on the very day.

Rather, it appears that this is the teaching: The mitzvah of confession on the eve of Yom Kippur—that one must confess in order to enter the holy day in repentance—is at nightfall, close to the day itself, so that there will be no time to sin between the confession and the day. But the Sages worried that his mind might be disturbed at the meal and that in his drunkenness he might withhold confession. Therefore, they required him to confess before eating. Still, he returns and confesses again at the proper time, at nightfall, close to the day itself, lest some sin occur at the meal. The confession of Ma’ariv, which is the confession of Yom Kippur itself, is not what this baraita teaches, for certainly he will confess on Yom Kippur. Rather, the baraita teaches that even if he confessed at Ma’ariv, he must confess at Shacharit, and all throughout the day, in case he sinned during Yom Kippur. With nightfall (Ne’ilah), the day brings atonement. This is the correct understanding of this baraita.

What further strengthens this interpretation is that I found explicitly in the Tosefta: “The mitzvah of confession on the eve of Yom Kippur is at nightfall. But the Sages said: A person must confess before he eats and drinks, lest his mind be disturbed during eating and drinking. And even though he confessed before eating and drinking, he must confess again after eating and drinking, lest some sin occur at the meal. And even though he confessed after eating and drinking, he must confess at Ma’ariv. And even though he confessed at Ma’ariv, he must confess at Shacharit… until he must confess at Ne’ilah, lest some sin occur during the entire day.” This is explicit.

Only, the Talmud did not teach in the baraita it cited the clause “even though” between the confession of erev Yom Kippur and the confession of Ma’ariv, for the reason we explained. But the Tosefta taught it explicitly, to clarify that even if one confessed close to Yom Kippur itself, he is not exempt from the Ma’ariv confession. But all of them intended one and the same thing: that one must confess before the meal, after the meal at nightfall, at Ma’ariv, and throughout the day.

Rashi, of blessed memory, explained “toward nightfall” to mean Ma’ariv, when the day has already been sanctified. But this is not the case anywhere. And none of the early authorities wrote in their works that one should confess twice on the eve of Yom Kippur, nor did they precisely analyze this baraita. What we have written here is the true, correct, and upright interpretation. May the God of truth, abundant in kindness and truth, answer us with truth, kindness, and mercy, and forgive our sins and our transgressions. Amen, may it be His will.

The mitzvah of confession (vidui) on the eve of Yom Kippur is at nightfall, immediately upon accepting the sanctity of the day. Nevertheless, the Sages instituted that one should confess before eating, lest drunkenness or some mishap occur during the meal and he would not confess properly. And even if he already confessed at Ma’ariv, he must confess in all the prayers of the day—Shacharit, Musaf, Minchah, and Ne’ilah.

Where is it recited? An individual recites it after his prayer, and the prayer leader (shaliaḥ tzibbur) recites it in the middle. The essence of the confession is: But we have sinned, etc., until “and it has profited us nothing.” However, it has become the custom to add ancient liturgical formulas dating back to the time of the Talmud, such as “You know the mysteries of the universe,” which we recite on Yom Kippur; and “Master of the universe,” which we recite every day; and “God, before I was created,” which we recite from Rosh HaShanah until Yom Kippur.

One must always precede the confession of unintentional sins to the confession of deliberate sins. That is why we say: “We have sinned, we have committed iniquity, and we have transgressed.” This is what they said: “Sins (ḥata’im) are inadvertent errors; iniquities (‘avonot) are intentional sins; transgressions (pesha’im) are rebellious acts.”

Similarly, one must confess while standing and with bowing, as it was said in this very sugya regarding Mar Shmuel: when the prayer leader reached “But we have sinned,” he arose—meaning, he stood up to confess together with the congregation.

It was taught by Ḥiyya bar Rav of Difti: The verse states: “And you shall afflict your souls on the ninth of the month.” Is the fasting on the ninth? But isn’t the fasting on Yom Kippur on the tenth of Tishrei? Rather, this verse comes to teach you: Whoever eats and drinks on the ninth, thereby preparing himself for the fast on the next day, the verse ascribes him credit as though he fasted on both the ninth and the tenth.

as though he fasted on both the ninth and the tenth.

“The order of the Eveof Yom Kippur(the Day of Atonement)” - Containing two paragraphs.
It is a commandment to eat on the Eve of Yom Kippur and to increase (one’s eating) at the meal.
Hagah: It is forbidden to fast on it (the Eve of Yom Kippur), even a dream fast (due to a nightmare), (מהרי״ל). And if one vows to fast on it, see above (in the Shulḥan Arukh, Oraḥ Ḥayyim), chapter 570, paragraph 2.

The wording of the sugya as it stands before us is: The mitzvah of confession (viduy) on the eve of Yom Kippur is at nightfall. But the Sages said: A person should confess before he eats and drinks, lest his mind become confused. Yet, according to this, the mitzvah of confession on the eve of Yom Kippur remains at nightfall (meaning: after he has eaten and drunk). However, the Sages added, because of the concern that his mind may become confused, that he should also confess beforehand. For they do not actually disagree about this at all, and indeed the Ramban, of blessed memory, derived his position from this—that one is obligated to confess at nightfall. As he said: It seems that the teaching means that the mitzvah of confession on the eve of Yom Kippur is at nightfall, i.e. after eating and drinking; but the Sages required him to confess earlier, before eating, lest his mind become confused during the meal. And on this he commented: Although they required him to confess earlier, still the essential confession did not lose its proper place, etc. See there.

[And I have noted here the words of the Baʿal Halakhot Gedolot (Bahag), which I have not seen cited elsewhere, that are explicit against the Ramban. He wrote that after one has confessed these six confessions (the one before eating, plus the five of Yom Kippur itself), a person is assured that his sins between himself and God are forgiven, etc. Clearly, this does not align with the Ramban’s view.]

And yet, our Master (Rabbenu, i.e. the Rambam) did not at all mention the rule that the mitzvah of confession is at nightfall. (See the Jerusalem Talmud at the end of tractate Yoma: The mitzvah of confession on the eve of Yom Kippur is at nightfall, before one becomes immersed in food and drink. It seems there that even before eating, it is called “at nightfall,” which requires clarification.)

And see this: I found in the Rif’s text that the version of the baraita is: The Sages taught: The mitzvah of confession on the eve of Yom Kippur is at nightfall, these are the words of Rabbi Meir. But the Sages say: One must confess before he eats and drinks, lest some mishap occur at his meal, etc. Behold, the Sages disagree with Rabbi Meir, who holds that the mitzvah of confession is at nightfall, whereas they hold that the mitzvah is before eating. And these are the words of our Master (the Rambam): that the mitzvah of confession of Yom Kippur begins on the eve of the day before he eats, following the view of the Sages over Rabbi Meir. And according to this version, the other matters upon which the Ramban stood are also precise, such as in the statement: Although he confessed before he ate, he should confess again in the evening prayer. Would you think that because he confessed before Yom Kippur, he should not confess on Yom Kippur? Behold, the essential confession is on Yom Kippur. And according to our Master and his version, this too is perfectly precise: that the essential mitzvah of confession, according to the Sages, is on the eve of Yom Kippur before eating, and this itself counts as the Yom Kippur confession and its essential fulfillment. And yet, he is also obligated to confess on Yom Kippur itself, at every prayer.

And from the words of the Tosafot Yeshanim it also seems that they had this version, that the Sages disagreed with Rabbi Meir. And see in the Agudah on Yoma, where he wrote: The mitzvah of confession on the eve of Yom Kippur—the Sages say one must confess before he eats and drinks. There is room to suppose that his version was also like that of the Rif, as we have brought, though it is not certain. And see in the Yereim, section 121, who likewise brought the Rif’s version: Rabbi Meir says … and the Sages say …

And one must confess at Minḥah (the afternoon prayer) before the concluding meal, as it was taught: The mitzvah of confession on the eve of Yom Kippur is at nightfall. But the Sages said: He confesses before eating, lest his mind become confused because of the meal and he will not be able to confess afterward.

And one must confess at Minḥah (the afternoon service) before the final meal, as it was taught: The mitzvah of confession on the eve of Yom Kippur is at nightfall; but the Sages said: He should confess before eating, etc. This wording of the baraita appears in the Tosefta at the end of tractate Yoma. And in the Gemara, in the last chapter of Yoma (87b), it states as follows: The Sages taught: The mitzvah of confession on the eve of Yom Kippur is at nightfall, these are the words of Rabbi Meir. But the Sages say: He must confess before he eats and drinks, lest some mishap occur at the meal. And even though he confessed at Ma’ariv (the evening service), he confesses again at Shaḥarit, etc.

And the Ran wrote: The mitzvah of confession on the eve of Yom Kippur is at nightfall, after eating, once he has accepted upon himself Yom Kippur. Since there may occur some mishap such as drunkenness or the like, he must confess after he has eaten and drunk, in the evening prayer. So explained the earlier authorities. But the Ramban challenged them, and explained instead that the intent is this: The mitzvah of confession on the eve of Yom Kippur, meaning that one must confess before entering the day, in repentance, is at nightfall, close to the day itself—so that there not be time to sin between the confession and the day. But the Sages were concerned that perhaps his mind would become confused at the meal, and his drunkenness would prevent him from confessing. Therefore they imposed on him the stringency to confess before eating. And even though he confessed before eating, he must confess again at its proper time, at nightfall, close to the day itself—lest some mishap of sin occur during the meal.

But the confession of Ma’ariv, which is the confession of Yom Kippur itself, was not included in this teaching—for certainly one confesses on Yom Kippur. Rather, it was teaching: Even though he confessed at Ma’ariv, he must confess again at Shaḥarit and throughout the day, lest he sin during the day; for Yom Kippur at its end, at nightfall, effects atonement.

And Ramban brought a proof to his words, from that which is taught in the Tosefta: "The mitzvah of confession on the eve of Yom Kippur is at nightfall; and even though he confessed before he ate and drank, he must confess after eating and drinking, lest some mishap occur at the meal. And even though he confessed after eating and drinking, he must confess at Ma’ariv; and even though he confessed at Ma’ariv, he must confess at Shaḥarit."

But the common practice is not in accordance with the words of the Ramban.

“The order of confession (of sins)during Minḥah(the Afternoon Prayer) on the Eve of Yom Kippur” - Containing six paragraphs.
One needs to confess during Minḥah (the Afternoon Prayer) before the (last) meal before fasting.
Hagah: If one is alone he says it (the confessional) after he finished his Silent Prayer, but the public reader says his (confessional) on Yom Kippur during the Silent Prayer, (טור).

“Before the meal" - Lest something untoward happen during the meal, and he will not be able to confess.

"Before the concluding meal" – lest something untoward happen to him during the meal, that he might choke or lose his mental clarity, and he would then be unable to confess afterward. And there are decisors who hold that one must also confess after eating, before nightfall, and it is proper to be stringent according to this view (Shelah). And so is the practice in our times, that one recites Tefillah Zakkah then.”