After researching the Bab’s writings, Stephen Lambden concluded that the Bab claimed the Prophet Muhammad publicly announced his Prophethood 7 years before Hijrah, after a number of years of private preaching. Lambden claimed: “The total value of all the disconnected letters from A.L.M. to A.L.M.R is thus 1267. It is evident that, taken as years of the Islamic lunar calendar (this calculation is based on the lunar, not solar calendar) yields 1267 which is 7 years in excess of 1260 (1260/1844). This seeming discrepancy can be resolved in the light of the Bāb’s presupposing that the public commencement of the mission of the prophet Muhammad was about 7 years prior to the flight to Medina (Hijra, 1 A.H. = 622 C.E.) when the Islamic calendar begins. Account must then be taken of the fact that Muhammad did not proclaim his mission publicly for a number of years after his call to Prophethood at the time of his encounter with the angel Gabriel on Mount Hira (c. 610 CE or later?). These details were early on utilized in Bābī-Bahā’ī teaching activity. The great Bahā’ī apologist Mīrzā Abu’l-Faḍl Gulpāyigānī, for example, clarified and used this Islamic proof text in several of his writings including his early Sharḥ-i āyāt-i muvarrikhih (“Commentary upon the chronological proof texts”) which was written in Hamadān (Irān) around 1888 CE.” 
Abdul Baha claimed that Prophet Muhammad publicly announced his Prophethood 10 years before Hijrah, after 3 years of private preaching. Abdul Baha claimed: “Afterwards, in verses 11 and 12, it is said: ’And from the time that the daily sacrifice shall be taken away, and the abomination that maketh desolate be set up, there shall be a thousand two hundred and ninety days. Blessed is he that waiteth, and cometh to the thousand three hundred and five and thirty days.’
The commencement of this lunar reckoning is from the day of the proclamation of the prophethood of Muḥammad in the land of Ḥijáz; and that was three years after the revelation of His mission, because in the beginning the prophethood of Muḥammad was concealed, and no one knew of it save Khadíjih and Ibn-i-Nawfal, until it was publicly announced three years later. And it was in the year 1290 from the proclamation of the mission of Muḥammad that Bahá’u’lláh announced His Revelation.” 
So Abdul Baha claimed that Bahá’u’lláh announced His Revelation in 1280 Hijri (Islamic Lunar Calendar) but the Prophet Muhammad publicly announced his Prophethood 10 years before Hijrah, so therefore ‘1290 days’ in the Bible refers to this.
These conflicting narratives regarding the timing of the public announcement of Prophet Muhammad’s prophethood within Bahá’í texts offer an opportunity for further exploration and discussion.