There are 571 years between the Prophet Jesus (as) and the Prophet Muhammad (saas), Ulu al-'azm Prophets (the Resolute Messengers), and Hazrat Mahdi (as) will come some 400 years after Imam Rabbani

Some people think that the fact that Hazrat Mahdi (as) will come some 400 years after Imam Rabbani will somehow diminish the worth of Imam Rabbani and claim that Hazrat Mahdi (as) will come 1000 years after the imam. The fact is, however, that Hazrat Mahdi’s (as) coming around 400 years after Imam Rabbani in no way diminishes his value. Allah sent our Prophet (saas) just 571 years after the Prophet Jesus (as), a Resolute Messenger. The Prophet Muhammad (saas) came soon after the Prophet Jesus (as), with a new law and book. In other words, there are 571 years between the two Resolute Messengers. Hazrat Mahdi (as) will come some 400 years after Imam Rabbani. Indeed, Imam Rabbani declared as such himself, saying that Hazrat Mahdi (as) will come 1000 years after the death of our Prophet (saas):

The end of this Ummah will begin WITH THE BEGINNING OF THE SECOND THOUSAND. IN OTHER WORDS, AFTER THE DEATH OF RASULULLAH... The full implementation of the moral values of the Qur’an and the renewal of the Islamic world IS IN THIS SECOND THOUSAND. THE JUST WITNESSES OF THE TRUTHFULNESS OF THIS CASE ARE THE EXISTENCE OF JESUS (AS) AND THE MAHDI (AS) IN THIS MILLENNIUM (IN OTHER WORDS, IN THE THOUSAND YEARS FOLLOWING THE DEATH OF OUR PROPHET (SAAS)).  (Imam Rabbani, Letters of Rabbani, p. 261)

Here, Imam Rabbani is clearly and explicitly speaking of NOT AFTER HIS OWN DEATH, BUT AFTER THAT OF OUR PROPHET (SAAS).

As Imam Rabbani says, the end of the Islamic world will begin with the second millennium and Imam Rabbani, the Prophet Jesus (as) and Hazrat Mahdi (as) will be in the second millennium after the death of our Prophet (saas).