The Revelation 12 SIGN , unique in celestial history , was first noticed by Scottie Clark. What he ( and the rest of us ) missed in Revelation 11 may be significant.
First, the Lord promised that we who watch would "know" the hour. Rev 3:3
Second, Revelation 11 , immediately preceding the Revelation 12 "Sign" discusses "silence for half an hour in the heavens". Since we are neither in the heavens nor can we hear silence , it follows that the following chapter 12 celestial sign is the marker for us to measure "silence in heaven" from.....
Third, this view utilizes the 7 mentions of "earthquake" in the book to correlate the events described in Revelation into two groupings -- placing Chapters 8-11 as God's line and chapters 12-20 as Satan's line. The earthquake descriptions do seem to justify this arrangement and timeline.This leaves an overlap of a "half hour" the period of silence in heaven , a time period which follows the celestial sign of Sept 23, 2017. (Rev 12). That time overlap is currently at over 5 years and 3 months using 365 day count years. ( However , both Revelation and Daniel use 360 count years).