I believe that opening up the Book refers to a Book that had been sealed.
I believe that this is the time of the end and the Bab and Baha'u'llah unsealed the book.
The "Book" is the Bible that was intended to be sealed up until the time of the end
, until the thousand three hundred and five and thirty days came. The 2,300 years came in
1844 and the book was unsealed by the Bab and Baha’u’llah. That math is explained in Some Answered Questions,
10: TRADITIONAL PROOFS EXEMPLIFIED FROM THE BOOK OF DANIEL
Daniel 12
King James Version
4 But thou, O Daniel, shut up the words, and
seal the book, even to the time of the end: many shall run to and fro, and knowledge shall be increased.
8 And I heard, but I understood not: then said I,
O my Lord, what shall be the end of these things?
9 And he said, Go thy way, Daniel:
for the words are closed up and sealed till the time of the end.
10 Many shall be purified, and made white, and tried; but the wicked shall do wickedly:
and none of the wicked shall understand; but the wise shall understand.
11 And from the time that the daily sacrifice shall be taken away, and the abomination that maketh desolate set up,
there shall be a thousand two hundred and ninety days.
12
Blessed is he that waiteth, and cometh to the thousand three hundred and five and thirty days.