I was talking to a friend of mine in the beis medrash and he mentioned that all the meforshim agreed that Moshiach had to come by 6000 and according to the Rambam we really are only 70 years or so from that date. My personal feeling is that there is a good reason to not try and figure out when Moshiach will come and publicize it, the fact that you will usually end up being wrong. Since he felt it was a 100% certainty he felt that there was no risk in teaching this fact to our children. Now I personally feel that there is a tremendous risk in teaching this at all, especially teaching that if he comes he must come by 6000. First it seems very strange to assume that G-d would assign special significance to 6000 a number which only has value in a decimal system. Secondly the shock that Shabbatai Tzvi’s lies caused to Judaism would seem like nothing compared to the number of people who would go off the derech immediately a number which could reach 50% (no exageration). Secondly even if all the calculations are right and the real Messiah comes in 6000 how will we know who he is, we’ll be drowning in false Messiahs every unscrupulous Jew born on tisha bav will be looking for his following and his chance at being the Moshiach the best possible outcome is unbelievable confusion and the worst is the end of Judaism as we know it.