"And the beast that was, and is not, even he is the eighth, and is of the seven, and goeth into perdition."
The 7th kingdom is not part of this beast at all. The 7th head is the temporary 8th kingdom.
Revelation 12 is the historical relationship between Satan and the statue of Daniel 2. Revelation 13 is the historical relationship of this statue with humanity. Revelation 17 is the historical relationship of this statue with religion. The ten kings never have a kingdom, but are ten humans arising during the Trumpets and Thunders who bring their nations and armies to side with Satan in some coalition that literally wipes out all religion on earth, and attempts to reconcile humanity with Satan against Jesus Christ without religion.
"And the ten horns which thou sawest are ten kings, which have received no kingdom as yet; but receive power as kings one hour with the beast. These have one mind, and shall give their power and strength unto the beast. These shall make war with the Lamb, and the Lamb shall overcome them: for he is Lord of lords, and King of kings: and they that are with him are called, and chosen, and faithful."
So it would seem that the stone started out during the 4th kingdom at the Cross, and grew to finally obliterate the 5 kingdom statue, around the time of the Reformation. It thus grew into a mountain filling the whole earth, the effect of the Gospel taken to the whole earth, and every nation. The 6th Kingdom was defunct as no single nation ruled the earth.
At the Second Coming, the 6th Seal, the 6th Kingdom is brought to life by Satan. That kingdom ends at the 7th Trumpet, when Jesus is declared King of the 7th kingdom.
In the midst of the week of days of the 7th Trumpet, God will either allow Satan 42 months as the 8th kingdom, or not.
So John left the first century, because what he was a witness to was not about the first century. Even the 19th century was in the past, according the present John was witnessing.