29Men and brethren, let me freely speak unto you of the patriarch David, that he is both dead and buried, and his sepulchre is with us unto this day.
Acts was written during the apostolic period between Christ's resurrection and His return in judgement on Jerusalem.
Now follow me closely here...
The resurrection of the saints (literally "holy ones") was for Daniel and his people:
{1} "Now *
at that time Michael, the great prince who stands
guard over
the sons of your people, will arise.
And there will be a time of distress such as never occurred since there was a nation until that time; and at that time your people, everyone who is found written in the book, will be rescued.
{2} "Many of those who sleep in the dust of the ground will awake, these to everlasting life, but the others to disgrace and everlasting contempt. Daniel 12:1-2 (NASB)
*This vision from God is given to Daniel for "his people" and it refers to
"the end of the age."
{13} "But as for you, go
your way to the end; then
you will enter into rest and rise again for your allotted portion
at the end of the age."
Daniel 12:13 (NASB)
In verse 13, Daniel is told to go his way until the end of his life, then he would "enter into rest" and "rise again at the end of the age" where he would receive his reward ("allotted portion.")
(On a side note, here in verse 13 you have a picture of the Greek view of death (Thanatos), "rest" (Hades), and resurrection, but I digress).
So the question is, what is the end of the age and when did it come?
The NT gives us clues:
{11} Now these things happened to them as an example,
and they were written for our instruction, upon whom the ends of the ages have come. 1 Corinthians 10:11 (NASB)
{26} Otherwise, He would have needed to suffer often since the foundation of the world;
but now once at the *
consummation of the ages He has been manifested to put away sin by the sacrifice of Himself.
Hebrews 9:26 (NASB)
(*Completion, perfection, fulfillment.)
{6} Yet we do speak wisdom among those who are mature; a wisdom, however,
not of this age nor of the rulers of this age, who are passing away;
{7} but we speak God's wisdom in a mystery, the hidden
wisdom which God predestined before the ages to our glory;
{8} the wisdom which none of the rulers of this age has understood; for if they had understood it they would not have crucified the Lord of glory;
1 Corinthians 2:6-8 (NASB)
The "end of the age" is when the resurrection of Daniel's people occurs, and in all of the verses cited above, Paul makes it clear that the people to whom he was writing were living during that time.
Therefore, the resurrection of Daniel and his people coincides with the destruction of Jerusalem and the temple in 70 AD, when the smallest letter and stroke of the Law was fulfilled:
{18} "For truly I say to you,
until heaven and earth pass away, not the smallest letter or stroke shall pass from the Law until all is accomplished. Matthew 5:18 (NASB)
{21} "For then there will be a great tribulation, such as has not occurred since the beginning of the world until now, nor ever will.
Matthew 24:21 (NASB)
And there will be a time of distress such as never occurred since there was a nation until that time...
Daniel 12:1
In conclusion, the resurrection was for Daniel and his people coming at the end of the age, when the smallest letter and stroke of the Law would be fulfilled. That happened in 70 AD. When Acts was written, Daniel was still in the grave. He was not there after Jerusalem and the temple fell: he was raised from the dead and given an incorruptible body, just as every Christian today will get the moment we pass "from life to life."
Daniel and his people died and slept in the ground while their souls languished in Hades. Hades was fully emptied at the "end of the age" of the Law and remains empty to this day, as the souls of the righteous go straight to the Father when we die:
{21} For to me, to live is Christ and to die is gain.
{22} But if
I am to live
on in the flesh, this
will mean fruitful labor for me; and I do not know which to choose.
{23} But I am hard-pressed from both
directions, having the desire to depart and be with Christ, for that is very much better;
Philippians 1:21-23 (NASB)
The moment a believer leaves the flesh he or she enters the presence of Christ. There is no more "resting" in Hades. We will all "rest" in Christ.
Hope this helps.