But that's the Bible. The 1260 years is also the Bible. What predictions of the date do Baha'is have from the Quran?
In Shia Islam the year AH 1260 was significant, it was also independent of any Biblical reference. The Shia branch of Islam (the Bab and Baha'u'llah were of the Shia line) followed a series of 12 Imams. The authority of the 12 Imams traced back to Muhammad. The last of the Imams disappeared in the Islamic year 260 AH.
According to a reference in the Qur'an 32:5 authority was to be re-established after 1,000 years. Thus there was widespread anticipation among Shi'ites that the 12th Imam would return in Islamic year 1260 AH. This is also the year 1844 AD in the Christian calendar.
Many Muslim Divines that knew of this Prophecy, did accept the Bab.
The wiki link has interesting references about how some ministers saw how Christ might rerurn, described how it has happened and is happening quite visionary
Day-year principle - Wikipedia
"The following is an excerpt from "the Covenanter", a Reformed Presbyterian publication (1857):
“The end of the 1260 years will not at once usher in the brightness of the Millennial day. It will be marked by some occurrence, by some grand movement of Providence—such as the violent, it may be, and sudden crushing of the Papal power, and that of the corrupt and oppressive monarchies of the Old World, and of the governments similar to them in spirit, if not in form, in the New-— by some event in the pagan world, in which a new era will take its rise: new and signally successful efforts for the conversion of the Jews—for the evangelization of the nations-—for the subjecting of the “kingdoms of this world” to the law and government of “the Lord and of his Christ.” A generation may pass, or more than one, before this work will be fully completed; but it will advance with large strides.”
Another that is saying a gradual unfolding, but note this one has a vision about the rulers to which Baha'u'llah has said He has seized all power from them;
Henry Folbigg (1869) wrote, "
It is here predicted that after the destruction of the papal beast, “the rest of the beasts,” by which I understand the Pagan, Mahometan, Hindoo, Chinese, and other empires, “ will have their dominion taken away,” that is, they will gradually lose their dominion, perhaps be conquered and lose their heathen rulers— “ but their lives ”—the existence of various corrupt "and unchristian principles, “ will be prolonged for a season and a time,” which, if intended to be taken in the usual prophetic and symbolic sense would indicate a period of 450 years. This would extend far into the Millennium, and therefore although we may and should look for, and hasten the coming of great and beneficial changes, we are not to expect universal civilization in a day, nor the conversion of the world in a year—but rather the gradual yet more rapid spread of the gospel and the spiritual reign of Christ and his saints—of Christ and his Church for 1,000 years"
Baha'u'llah wrote to the Pope and the Catholic Church lost its power in the Mid 1800's, that history is available.
Regards Tony