Gemara

(Beraisa): "Ki Azlas Yad v'Efes Atzur v'Azuv" - Ben David will not come until there are many informers. Alternatively, he will not come until Talmidim diminish, or until people lack money, or until they despair of redemption.

When R. Zeira would see people speculating about the Ketz (when Moshi'ach will come), he would say 'please do not delay him';

(Beraisa): Three things only come through Hesech ha'Da'as (ceasing to think about them) - Moshi'ach, a Metziah, and a scorpion (bite).

97b (Beraisa - R. Noson): "Ki Od Chazon la'Mo'ed; Im Yismahme'ah Chake Lo" - we cannot know for sure when Moshi'ach will come.

Do not rely on Chachamim who expound "Ad Idan v'Idanin u'Flag Idan" (Daniel said that Moshi'ach will come after 1400 years), or on R. Simlai who expounds "va'Tashkemo bi'Dma'os Shalish" (it will be after 1410 years).

Question: What does it mean "v'Yafe'ach la'Ketz v'Lo Yechazev"?

Answer (R. Shmuel bar Nachmani): Tifach (should be bloated) people who calculate Ketz ha'Moshi'ach, for they say that if he does not come by their predicted date, he will never come. Rather, "Chake Lo" (wait for him).

Midas ha'Din is delaying Moshi'ach. We wait for him in order to receive reward - "Ashrei Kol Chochei Lo."

Kesuvos 111a (R. Yosi b'Rebbi Chanina): Shir ha'Shirim alludes to three oaths that Hash-m imposed: Yisrael may not return together to Eretz Yisrael by force; Yisrael may not rebel against the other nations; and the nations should not subjugate Yisrael too harshly.

(Rav Yehudah): "If you will awaken, if you will arouse" shows that there were more oaths!

R. Zeira learns the additional oaths like R. Levi:

(R. Levi): The three additional oaths forbid revealing the Ketz, distancing the Ketz, and revealing the secret to the nations.

Megilah 3a: Yonasan ben Uzi'el was allowed to reveal the translation of Nevi'im, but not of Kesuvim, for it contains Ketz ha'Moshi'ach.

11b (Rava): Belshatzar erred (about when the 70 years of exile before rebuilding the Mikdash are completed). He counted from 'l'Malchus Bavel', not from "l'Bavel" (the first exile to Bavel). Also Achashverosh erred. He counted from Galus Yehoyachin, instead of from the Churban of Yerushalayim.

Also Daniel miscalculated - "Ani Daniel Binosi bi'Sforim."

Shabbos 31a (Rava): A person is asked six things when brought to judgment (after death)... did you anticipate Yeshu'ah (salvation)?

Bava Metzia 85b: Once, Eliyahu told Rebbi 'I woke Avraham, and set him down again after he prayed. I did the same for Yitzchak, and then for Yakov. If I would wake them (and they would pray) together, this would bring Mashi'ach prematurely. R. Chiya and his sons have a similar power of prayer.

Rebbi asked R. Chiya and his sons to lead the prayer. When they were about to conclude 'Mechayeh ha'Mesim', the world shook. Eliyahu was punished for revealing their power of prayer. He distracted them from praying.

Rishonim

Rambam (Hilchos Melachim 12:2): Some say that a Navi will come to return Yisrael in Teshuvah before the war of Gog and Magog... Some say that Eliyahu will come before Moshi'ach... No one can know these things until they will be. It is not clear from the Nevi'im, and Chachamim do not have a tradition. It is not important for us to know the order of events. A person should not make them primary, for they do not lead to love or fear of Hash-m. Similarly, one should not calculate Ketzim. Chachamim said that people who calculate Ketzim should be bloated. Rather, one should wait and trust that it will occur.

The Rambam (Igeres Teiman 283 p.152, cited in Gilyon of Frankel Rambam) says that Rav Sadya Gaon calculated a Ketz even though he knew that this is forbidden. His generation had corrupt ideas and he needed to bolster them lest Torah be forgotten. The Rambam (ibid. p.176) cites a Ketz that he received from his father.

Rashi (Kesuvos 111a DH she'Lo): Nevi'im in Yisrael are forbidden to reveal the Ketz.

Ya'avetz: Perhaps shortly before the Ketz, the Ketz will become known to Yisrael, like Yo'el propecized "your sons and daughters will be prophets."

Rashi (111a DH veshe'Lo): We are commanded not to distance the Ketz through sins. Alternatively, some texts forbid to be Dochek the Ketz, i.e. too request about it too much.

Maharsha: Alternatively, we may not distance the Ketz, i.e. we should not think that it is a long time away and despair from redemption.

Anaf Yosef (in Ein Yakov Kesuvos 11a): Something that comes in its time has been properly clothed in nature, and there is no prosecution against it. It will come smoothly, without pain. If people pray too much, Hash-m will accede and bring the redemption early, but there will be prosecution and it will come amidst great pain and suffering.

The Ramban (Bereishis 3:2) calculates a Ketz. The Chasam Sofer (Teshuvos 6:61) disagrees with the Ramban's calculation and says that at the earliest, the Ketz must be about 400 years later.

Chasam Sofer (Kovetz Teshuvos 26:4): Long ago, some made calculations and said that certain things will happen when the planets are aligned. Many Yisre'elim with solid Emunah believed in this. The Abarvenel on Daniel (Mayanei ha'Yshu'ah 12, 2:1) calculated Ketz ha'Mashi'ach through this. We find many similar matters in the Ibn Ezra, Ralbag, and many like them.

Kad ha'Kemach (of R. Bechayei, Sof Ge'ulah): It says in Daniel (12:12) "Happy is he who waits for the days 1,335". It is known that there are three Ketzim for our Galus, just like there were for Galus Mitzrayim.

Acharonim

Maharsha (Sanhedrin 97b DH Anu): The Gemara asked 'why should we wait for Moshi'ach?', because Moshi'ach will come only through Hesech ha'Da'as.

Iyun Yakov (Sanhedrin 97b DH Tifach): The punishment for people who calculate Ketzim (Tifach Atzmosav) is the ruining of the bone from which the dead will be revived. When their dates pass and Moshi'ach did not come they despair, therefore they will not be revived.

Margoliyos ha'Yam (Sanhedrin 97b 10): The Isur to calculate the Ketz applies only to people who say that if he does not come by their predicted date, he will never come. People who believe that he surely will come may calculate the Ketz to invigorate the wavering. Many Gedolei Yisrael did so. Often, great salvations occurred in the predicted times, but the generation was not worthy for it to be the ultimate Ge'ulah. "Madu'a Lo Va Ven Yishai El ha'Lechem Gam Temol Gam ha'Yom?" "Madu'a Lo Kilisem Chokchem... Gam Temol Gam ha'Yom?"! (Moshi'ach did not come because Yisrael did not fulfill their obligation.

Mishneh Halachos (11:1): R. Zeira criticized speculation about when Moshi'ach will come. He forbidsden to be Dochek the Ketz. Rava taught that one will be asked 'did you anticipate Yeshu'ah'? It is proper or obligatory to pray for the redemption in Tikun Chatzos, at the ends of the each thirds of the night, in Korbanos, in Pesukei d'Zimrah, in Birkos Kri'as Shema, in six Berachos of Shemoneh Esre, and afterwards, in Tachanun, in u'Va l'Tziyon, in Aleinu, before and in Birkas ha'Mazon, in Al ha'Michyah... The entire day we pray for redemption! Perhaps the Halachah does not follow R. Zeira. Alternatively, the Isur to be Dochek the Ketz is to use names of Hash-m or impose oaths on angels to force the Ketz to come. The Magid of Koznitz said that he could force the Ketz to come in this way, but it is not Hash-m's will. Alternatively, surely R. Zeira agrees that one must pray for redemption. He objected to calculations of when Mashi'ach will come. Yakov Avinu wanted to reveal the Ketz, and Hash-m withheld it from him! (Rashi Bereishis 49:1). Mashi'ach will come only amidst Hesech ha'Da'as, i.e. when one feels that he needs to pray again. If the Avos would pray together, this would bring Mashi'ach prematurely. This shows that one may prompt Mashi'ach to come early through prayer. Rebbi tried to do similarly! One must pray even for individuals, all the more so for Mashi'ach and the end of the afflictions of the Rabim!