After not having focused on his return in his address to the first five, in the sixth and seventh Churches, Philadelphia and Laodicea respectively, we see that Jesus hints that his Return is immanent.
To Philadelphia he says,
I am coming soon. Hold on to what you have so that no one can take away your crown. (Rev 3:11)
Then to Laodicea he says,
Listen! I am standing at the door and knocking! (Rev 3:20)
And so it seems like that in the time of Philadelphia Jesus is on the way to the house, the Church on Earth, approaching quickly so to speak. But when Laodicea succeeds Philadelphia, Jesus is standing at the door and knocking, indicating that he will Return from Heaven in the time of Laodicea.
I also noticed that Jesus gives a singular favor to Philadelphia. He promises Philly that he will "keep them from the hour of temptation, which shall overcome the whole world in order to test those living upon the earth." This hour of temptation which will overcome the whole world seems to clearly reference the reign of Antichrist. This time of Antichrist's reign is brief less than a decade and so Jesus fittingly uses the figure of an hour. This is in opposition to the tribulation for ten days in the Church of Smyrna which I think represents ten major persecutions led by ten Roman Emperors in the nascent Church. Some of these Roman Emperors reigned for two decades, for example Diocletian from 284 to 305 in addition to the general persecution lasting for centuries with the intensity increasing and decreasing pending emperor. Antichrist on the other hand will overcome the whole world for no more than seven years, and then Jesus will return. Jesus will prevent the Church of Philadelphia from the advent of Antichrist, but he will not prevent Laodicea.