The book of Revelation gives us a time line of events, which will take place during the End of Days — the period of time that will directly precede the return of Christ. Given the nature of prophecy, it is not a clear cut process, however, I believe there is enough clarity for us to discern where we are in that time line.
The End of Days begins with the release of the rider on a white horse — the one who will prepare the way for the coming Beast. I believe this horseman was released decades ago, and his victories continue to build momentum as we come closer to the rise of the Beast. I have argued that we have received confirmation that the fourth rider(s) has been released — Death and Hades — as a UN report confirms that over a quarter of the world has been engulfed in conflict serious enough to produce refugees fleeing the war zones. Once released, the horsemen work relentlessly, and the impact of those efforts grow with time — i.e. the chaos and death that Death and Hades will wreck on the world has only just begun.
I have previously posed the question on whether the 5th seal has been opened or not:
And when he had opened the fifth seal, I saw under the altar the souls of them that were slain for the word of God, and for the testimony which they held:
10And they cried with a loud voice, saying, How long, O Lord, holy and true, dost thou not judge and avenge our blood on them that dwell on the earth?
11And white robes were given unto every one of them; and it was said unto them, that they should rest yet for a little season, until their fellowservants also and their brethren, that should be killed as they were, should be fulfilled.
The particulars of this prophecy may be complex, but overall, the opening of the 5th seal portends a renewed persecution and slaying of Believers. There have been media reports of instances of Believers being slaughtered in the Middle East and Africa, and we have speculated whether this portends the opening of the 5th seal — a report by a group affiliated with the Catholic Church would seem to confirm that the 5th seal has been indeed opened:
http://www.theguardian.com/world/2015/oct/13/christianity-under-global-threat-persecution-says-report
For whatever may be deemed the catalyst for this slaughter of Believers, we can see that the martyrdom of Believers have increased globally. We should take this as confirmation that the 5th seal has been opened.
There is no way of knowing how long it will be until the 6th seal is opened, but I believe that when that does happen, the whole world will know:
And I beheld when he had opened the sixth seal, and, lo, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became as blood;
13And the stars of heaven fell unto the earth, even as a fig tree casteth her untimely figs, when she is shaken of a mighty wind.
14And the heaven departed as a scroll when it is rolled together; and every mountain and island were moved out of their places.
15And the kings of the earth, and the great men, and the rich men, and the chief captains, and the mighty men, and every bondman, and every free man, hid themselves in the dens and in the rocks of the mountains;
I have argued that a massive eruption of a supervolcano will be God’s way of manifesting the sixth seal (of course, this is only my opinion). Whether the Yellowstone Caldera blows or whether by some other means, when God chooses to manifest the opening of the 6th seal, it will serve as a warning sign to the world that Christ’s return is near — and that things will get worse for the world before things get better.