How long was the book of Daniel to be sealed up?

The book of Daniel was to be sealed until the time of the end. From Daniel's perspective around 500 B.C., that span would be about 2,500 years, during which the book would be closed up and not considered all that much.

Les explains that God told Daniel, "shut up the words and seal the book," meaning Daniel was to close the book and forget about it. The sealing was to last "even till the time of the end." From Daniel's vantage point about 500 B.C., that meant roughly 2,500 years during which the book of Daniel would be closed up and not considered all that much. At the time of the end, many shall run to and fro, and knowledge shall be increased.

Daniel 12:4

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.

How long was the book of Daniel to be sealed until the time of the end?

From Daniel's perspective around 500 B.C., the book was to be sealed until the time of the end, a span of about 2,500 years. God instructed Daniel to shut up the words and seal the book, meaning it would stay closed and not be considered much until the end time.