Island Man:
You make a good point. The disciples wanted to know when the destruction of the temple and Jerusalem that Jesus had just foretold. (Mt 23:33-24:2) Jesus was telling them in 24:4-8 that wars, earthquakes, famines and plagues would not be indicators of when the calamity would come.
Why give such a non-sign? It was because people of those days viewed such events, in particular, as harbingers of God's wrath. So Jesus is telling them that events such as those would not be an indication of 'When these things will be.' (24:3) The event that would indicate "when" was described in 24:15. And Jesus said that they could expect it before the then present "generation" 'passed away.' (24:32-34)
Revelation chapter follows a similar motif. Following Jesus' crowning in 33 AD, which begins the march to his return and his eventual conquering of all his enemies (vv.1, 2), it foretells wars (vv.3, 4), famines (vv.5, 6), and death by sword, famine, plagues, and wild beasts (vv.7, 8), all of which were typically viewed by people as indicators of God's wrath. (Timewise, these things would parallel the ousting of Satan in chapter twelve and the woe for the earth and sea that was foretold to occur as a consequence. Compare 12:7-12.)
Yet, the 'souls' that cry out for justice in verses 9-11 ask, 'When will justice finally take place?' They are not calculating when the end will come based on the wars, famines, etc that were just described. Their cry for justice inserted into the account, and the answer they are given indicated that something else ("the number was filled also of their fellow slaves . . . who were about to be killed") had to finish before then end came. Rev. 7:1-8 explains more of the details of that.
Incidentally, Matthew 24 is not describing the same things as Revelation 6. Matthew 24:4-35 specifically describes what would happen to the Jewish temple and the city of Jerusalem (including the Jewish nation). Revelation 6 describes from Jesus' crowning to his still future return. Yet a similar pattern to Matthew 24 exists in the Revelation 6 account. This causes many to think that Matthew 24 is describing the very same thing as Revelation 6. Matthew 24:4-35 is instructive in showing a pattern that is followed in Revelation, but problems occur if one tries to map the one over the other since the things in the Matthew account are specific to the 1st century.
Take Care