You are taking "the hour is coming, and now is" as one thing. It is two.
"And now is" — present, already underway as he spoke.
"The hour is coming" — future from the moment he said it, and we are not left guessing when that hour was. It was when Jesus speaks his words to those in the grave. Surely you would agree that happened when Christ died on the cross.
That puts two groups of dead in front of us:
The hour when Jesus spoke to the dead in the grave is when - "and they shall be raised, they that have done good unto the resurrection of life, and they that have done evil unto the resurrection of damnation."
- Living men, dead in their sins, hearing his word and passing from death to eternal life. That is the "now is."
- The dead in the graves, who were dead in their sins just as the first group was.
The hour coming that now is, came when Christ made atonement for sin, defeated death and resurrected from the grave. Because the hour that was coming and now is has come, all who hear the gospel of the Kingdom of God and believe through the power of the Holy Spirit are being spiritually enlightened (awakened as thou from slumber) and being born again now know and enter the Kingdom of God (SPIRITUALLY).
The dead (physically) in the physical graves have not and will not hear the voice of Christ calling them to physical life again until the hour that is coming when the last trumpet sounds.
Jesus did not descend into the graves to speak to the dead. He descended down into the graves to set free the Old Covenant faithful saints who had been held captive to death until after the cross and resurrection, before ascending with them to the Kingdom of God in heaven. After His body was three days and three nights in the grave, Christ descended down to set the captives free taking them as spiritual body/living souls with Him to heaven.
Ephesians 4:8-10 (KJV) Wherefore he saith, When he ascended up on high, he led captivity captive, and gave gifts unto men. (Now that he ascended, what is it but that he also descended first into the lower parts of the earth? He that descended is the same also that ascended up far above all heavens, that he might fill all things.)
Matthew 12:40 (KJV) For as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth.
John 20:17 (KJV) Jesus saith unto her, Touch me not; for I am not yet ascended to my Father: but go to my brethren, and say unto them, I ascend unto my Father, and your Father; and to my God, and your God.