No I have stuck to what I have offered and as such i see your replies as one of two possible motives.
You really do not get such a simple explanation, or
You keep trying to put information in that is not needed.
If it is the former, then this link;
Day-year principle - Bahaipedia, an encyclopedia about the Bahá’í Faith
"The year 1260 was significant in Shia Islam, independently of any Biblical reference. The Shia branch of Islam followed a series of 12 Imáms, whose authority they traced back to Muhammad. The last of these disappeared in the Islamic year 260 AH. According to a reference in the Qur'an,[6] authority was to be re-established after 1,000 years.[7] For this reason, 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.
Therefore, Baha'is understand the 1,260-day prophecies in both Daniel and in the Book of Revelation as referring to the year 1260 of the Islamic calendar [8] which corresponds to the year 1844 AD, the year the Báb pronounced himself to be a Manifestation of God and the year that the Baha'i Faith began."
See no starting point needed for the 1260 Prophecy. I have said many times above, the 1260 does not need and advent starting point. Plainly 1844 is 1260.
For the 1844 Prophecy has the starting point is BC457, which is obtained for the Old Testament, along with the 2300 years to make the calculation.
Revelation 9:15 also predicts 1844, but that also needs a starting point of 1453. The link explains that one.
There are others with a starting point.
Regards Tony