It is becoming increasingly evident to me, via the writings in Pirkei D'Rebbi Eliezer, that at least some of the Sages of the Mishnah knew when the Final Keitz would be. The chapter of Pirkei D'Rebbi Eliezer quoted in the latest post on Birkat HaChamah includes within it Rebbi Akiva, famous for, among other things, for being a supporter of Bar Kokhba as Moshiach.
I mentioned before that according to the GR"A, if we are worthy, Moshiach ben Yosef could have come any time after the year 4000 and reigned over us until the appointed time came for the arrival of Moshiach ben David. This is the GR"A's drash on the 2000 years of Moshiach from the Tana D'vei Eliyahu.
For reasons I will not discuss at this time, it is apparent that the count that we use today for years is 163 years behind the physical year count since the events of the Sixth Day when Adam HaRishon was created. If we adjust the year count for the Churban of Bayit Sheini, we receive a year in the 4th millenium, but Bar Kokhba's revolt is squarely in the 5th millenium.
I think from this that Rebbi Akiva believed Bar Kokhba to be Moshiach ben Yosef, who fought against Edom, worked towards the building of Yerushalayim, etc. However, as the Rambam says in the Mishneh Torah, he died due to sins.
That is to say that any Moshiach that comes before the final Keitz in our generation and dies, it is known that we did not have the proper level of zechut, and inversely the sins of the generation (as well as individual sins) caused the death.
From this we can interpret the statement of Rebbi Yochanan in Yerushalmi Taanit (4:5) that grass would grow from Rebbi Akiva's face and still Moshiach ben Dovid will not have arrived. Perhaps Rebbi Akiva agreed, the Final Keitz was indeed far off. Rebbi Akiva thought that the situation was ripe according to the merit of Am Yisrael to move in to the age of Moshiach ben Yosef, but his colleagues disagreed on this point. Every generation, indeed every year, has its own special level of Teshuvah necessary for us to merit the Geulah. Their Teshuvah isn't our Teshuvah. This level of National Teshuvah, whatever it may be at an appointed time, causes Am Yisrael to be successful in actions towards the Geulah. Anything less than this level, and things go according to the last date (for each of Moshiach's Footsteps).