I think the meaning of this quote is made clear two pages ahead:

“From the destruction of Jerusalem, Christ passed on rapidly to the greater event, the last link in the chain of this earth's history,--the coming of the Son of God in majesty and glory. Between these two events, there lay open to Christ's view long centuries of darkness, centuries for His church marked with blood and tears and agony. Upon these scenes His disciples could not then endure to look, and Jesus passed them by with a brief mention” (DA 630, 631).

If the church had been ready before, the date would have been fixed earlier, but from the beginning God knows when this date will be, because He knows when the church will be ready.

"But like the stars in the vast circuit of their appointed path, God's purposes know no haste and no delay. ... So in heaven's council the hour for the coming of Christ had been determined. When the great clock of time pointed to that hour, Jesus was born in Bethlehem" (DA 32).

If this was true for the first coming, why not for the second?

"We are not to know the definite time either for the outpouring of the Holy Spirit or for the coming of Christ. . . . Why has not God given us this knowledge?--Because we would not make a right use of it if He did. A condition of things would result from this knowledge among our people that would greatly retard the work of God in preparing a people to stand in the great day that is to come." – LDE 33

"But the day and the hour of His coming Christ has not revealed. He stated plainly to His disciples that He Himself could not make known the day or the hour of His second appearing. Had He been at liberty to reveal this, why need He have exhorted them to maintain an attitude of constant expectancy? There are those who claim to know the very day and hour of our Lord's appearing. Very earnest are they in mapping out the future. But the Lord has warned them off the ground they occupy. The exact time of the second coming of the Son of man is God's mystery." DA 632, 633

These quotes make clear that God knows the day and the hour of Christ's coming, but deliberately chose to conceal this knowledge from us.

"When the fruit is brought forth, immediately he putteth in the sickle, because the harvest is come." Christ is waiting with longing desire for the manifestation of Himself in His church. When the character of Christ shall be perfectly reproduced in His people, then He will come to claim them as His own.

It is the privilege of every Christian not only to look for but to hasten the coming of our Lord Jesus Christ, (2 Peter 3:12, margin). (COL 69)

This is exactly what I am saying! God gives the prophecys so that the generation can have the possibility of spreading the gospel into all the world and have the second coming tied to events in their time

One of it's problems is that God is powerless to affect the future. He can see what will happen, but He can't do anything to affect it.

Because the Second Coming can be hastened!

That doesn't make sense given that a)Ellen White often wrote that Christ "could have come before now" b)We have the privilege of hastening Christ's coming. If the date were fixed, neither of these things would be possible.

Matthew 24:36 But of that day and hour knoweth no man, no, not the angels of heaven, but my Father only.
37 But as the days of Noah were, so shall also the coming of the Son of man be.

Before I get back to the 2300 days in Daniel 8, I'd like to point out. I do not have the date, but there is a Signs of the Times article where Mrs. White says that Miller was right and that Jesus could have come on October 22, 1844,(if I recall correctly the words were something like "There was no reason why William Miller could not have diserned from the scripture the coming of the Lord") but she goes on to say that Jesus did not because he knew that too many were not ready so like with Nineveh, God gave them more time, and that instead of making fun of the Millerites they should have been greatful that God gave them more time.