In a chronological sense this is when John was first given the visions of all things that must come first before Christ returns. Just like Matthew 24 is an outline of those events, Revelations expands more on them as they are revealed to John.
Rev 1:3 Blessed is he that readeth, and they that hear the words of this prophecy, and keep those things which are written therein: for the time is at hand.
The time has always been at hand beginning with the resurrection of Christ and Him ascending up to heaven, but yet no one knows the day or hour of His return. He has given us many signs to watch for His return, especially Matthew 24:29-31 which says immediately after the tribulation of those days (meaning Gods great wrath during the seven trumpets and seven vial judgements) and Rev 19:11-21 as this is at the timing of the seventh trumpet sounding after many have taken the mark of the beast, Rev 13, as on the last day, John 6:40, Christ then returns to destroy the beast and false prophet casting them into the lake of fire and then we are caught up to Him, 1 Corinthians 15:51-58; 1 Thessalonians 4:13-18.
