When John wrote Revelation 10, he had Daniel 12 in mind. Daniel 12 talks about sealing up the words of the prophecy until the "time of the end" (Dan. 12:4). Then in Daniel 12:7 someone lifts up his hands and swears by the One who lives forever and ever (Rev. 10:5, 6) that there will be "time, times, and half a time." It sounds almost exactly like Revelation 10, except that in Revelation the phrase "time will be no more" replaces the cryptic time period.
The point of Revelation 10 seems to be that the time prophecies of Daniel have run their course. Revelation 10 brings us to the point when God would unseal the book of Daniel and God's final message (the "mystery of God") would go to the world. Both texts have a strong sense of an appointed time. So the sixth trumpet brings us to a period in earth's history in which the final events are about to take place.
During the nineteenth century students of the Bible ransacked the books of Daniel and Revelation, trying to understand where humanity stood in the course of human history. After careful study, some of them concluded that the time prophecies of Daniel would end around the year 1844. They naturally assumed that the phrase "time would be no more" meant the end of the world, the second coming of Jesus. However, they missed one tiny word in Revelation 10:7--"but."
In the Greek language this particular word for "but" portrays a strong contrast, even more emphatic than the English "but." It tells us that the time prophecies of Daniel did not bring the world to the very end, but only to the "time of the end."
In a way this is nothing new. God has always portrayed the end as near (see Rev. 1:3). At the same time God's Word has always contained the seeds of an even deeper understanding. The disciples of Jesus, for example, thought that He would come immediately after His resurrection (Acts 1:6-8). But He then explained to them that the gospel had to go to the whole world first.
The Millerites in the nineteenth century, likewise, thought that the closing up of Daniel's time prophecies had brought them to the end of the world. But God's people still had a mission to accomplish first (Rev. 10:11; 14:6, 7). So the bottom line for the Christian life is not timing the end, but living the motto of the U.S. Marine Corps: "Semper Fidelis"--Always Faithful.
Lord, I want nothing more than to be found faithful when You come.