Christ in His Sanctuary : The Scriptures Reexamined

When the time passed at which the Lord's coming was first expected,—in the spring of 1844,—those who had looked in faith for His appearing were for a season involved in doubt and uncertainty. While the world regarded them as having been utterly defeated and proved to have been cherishing a delusion, their source of consolation was still the word of God. Many continued to search the Scriptures, examining anew the evidences of their faith and carefully studying the prophecies to obtain further light. The Bible testimony in support of their position seemed clear and conclusive. Signs which could not be mistaken pointed to the coming of Christ as near. The special blessing of the Lord, both in the conversion of sinners and the revival of spiritual life among Christians, had testified that the message was of Heaven. And though the believers could not explain their disappointment, they felt assured that God had led them in their past experience.
Interwoven with prophecies which they had regarded as applying to the time of the second advent was instruction specially adapted to their state of uncertainty and suspense, and encouraging them to wait patiently in  the faith that what was now dark to their understanding would in due time be made plain....
In the summer of 1844, midway between the time when it had been first thought that the 2300 days would end, and the autumn of the same year, to which it was afterward found that they extended, the message was proclaimed in the very words of Scripture: “Behold, the Bridegroom cometh!”
That which led to this movement was the discovery that the decree of Artaxerxes for the restoration of Jerusalem, which formed the starting point for the period of the 2300 days, went into effect in the autumn of the year 457 B.C., and not at the beginning of the year, as had been formerly believed. Reckoning from the autumn of 457, the 2300 years terminate in the autumn of 1844.