Commentary for Menachot 11:9
שְׁתֵּי הַלֶּחֶם נֶאֱכָלוֹת אֵין פָּחוֹת מִשְּׁנַיִם, וְלֹא יָתֵר עַל שְׁלשָׁה. כֵּיצַד. נֶאֱפוֹת מֵעֶרֶב יוֹם טוֹב וְנֶאֱכָלוֹת בְּיוֹם טוֹב, לִשְׁנָיִם. חָל יוֹם טוֹב לִהְיוֹת אַחַר הַשַּׁבָּת, נֶאֱכָלוֹת לִשְׁלשָׁה. לֶחֶם הַפָּנִים נֶאֱכָל אֵין פָּחוֹת מִתִּשְׁעָה, וְלֹא יָתֵר עַל אַחַד עָשָׂר. כֵּיצַד. נֶאֱפֶה בְעֶרֶב שַׁבָּת וְנֶאֱכָל בְּשַׁבָּת, לְתִשְׁעָה. חָל יוֹם טוֹב לִהְיוֹת עֶרֶב שַׁבָּת, נֶאֱכָל לַעֲשָׂרָה. שְׁנֵי יָמִים טוֹבִים שֶׁל רֹאשׁ הַשָּׁנָה, נֶאֱכָל לְאַחַד עָשָׂר. וְאֵינוֹ דוֹחֶה לֹא אֶת הַשַּׁבָּת וְלֹא אֶת יוֹם טוֹב. רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל אוֹמֵר מִשּׁוּם רַבִּי שִׁמְעוֹן בֶּן הַסְּגָן, דּוֹחֶה אֶת יוֹם טוֹב וְאֵינוֹ דוֹחֶה אֶת יוֹם צוֹם:
<i>Shtei Halechem</i> [loaves] were eaten no sooner than two [days from their baking] and no later than three. How so? They were baked on the day before Yom Tov [Shavuot] and eaten on Yom Tov, which is two days. If Yom Tov fell after Shabbat, they were eaten on the third day. <i>Lechem Hapanim</i> [loaves] were eaten no sooner than nine days [after their baking] and no later than eleven. How so? They were baked on the eve of Shabbat and eaten the following Shabbat, which is nine days. If Yom Tov fell on the eve of Shabbat, they would be eaten on the tenth day. If the two days of Rosh Hashanah fell before Shabbat then they were eaten on the eleventh day, for [their baking] does not override Shabbat or Yom Tov. Rabban Shimon Ben Gamliel said in the name of Rabbi Shimon ben Hasgan: they do override Yom Tov but not the Fast Day [Yom Kippur].
Bartenura on Mishnah Menachot
English Explanation of Mishnah Menachot
The showbread was eaten never earlier than on the ninth day and never later than on the eleventh day. How so? [Normally] it was baked on the day before Shabbat and eaten on Shabbat [of the following week], that is on the ninth day. If a festival fell on the day before Shabbat, it would be eaten on the tenth day. If the two days of Rosh Hashanah [fell before Shabbat], it would then be eaten on the eleventh day.
[Baking] overrides neither Shabbat nor the festival.
Rabban Shimon ben Gamaliel says in the name of Rabbi Shimon, son of the deputy [high priest]: it overrides the festival but not the fast day (Yom.
This mishnah deals with when the two loaves for Shavuot and the showbread were baked and when they were eaten.
Section one: The two loaves for Shavuot were always baked the day before Shavuot, unless Shavuot fell on a Sunday, in which case they were baked on Friday. Therefore, the two loaves were always eaten either on the second day, or at the latest on the third day.
Section two: Normally, the showbread would have been baked the day before Shabbat, and eaten the following Shabbat, on the ninth day. If a festival came before Shabbat, then it would have been baked on Thursday and eaten on Shabbat, the tenth day, and if Rosh Hashanah, which was always two days, came before Shabbat, it would have been baked on Wednesday and eaten on Shabbat, the eleventh day.
Section three: The mishnah explains that the baking of these loaves never overrides Shabbat or the festival. Thus sometimes they will have to be baked earlier.
Rabban Shimon ben Gamaliel disagrees and holds that baking the bread could override the festival, but not Yom Kippur. For instance, if the first day of Sukkot falls on Friday, the showbread could be baked on Friday, but if Yom Kippur fell on Friday, the showbread would have to be baked on Thursday.