John and Doves,
The timing of the 7th seal.
Revelation 8:1 And when he had opened the seventh seal, there was silence in heaven about the space of half an hour. 2 And I saw the seven angels which stood before God; and to them were given seven trumpets.
"When he had opened the seventh seal". According to the original Greek text, there is no "had" in this verse.
The correct context is "When he opened the seventh seal, there was silence in heaven for about half an hour".
Concerning how long the "half hour" is, we find the clue in Revelation 3:10.
Revelation 3:10 Because thou hast kept the word of my patience, I also will keep thee from the hour of temptation, which shall come upon all the world, to try them that dwell upon the earth.
Jesus makes promise to Philadelphia church that he will keep the church from the hour of temptation, which is to try them that dwell upon the earth. "The hour of temptation" is 7 years tribulation. So the "half hour" in Revelation 8:1 is 3.5 years or simply the first half of tribulation. Having said this, Jesus shall open the 7th seal in the middle of tribulation. The reason is because in the middle of tribulation, Jerusalem is under siege by gentiles nations. Jesus opens the 7th seal to bring forth the 7 trumpets judgment, in order to punish these nations who are gathered against Jerusalem.