15 And the four angels who had been kept ready for this very hour and day and month and year were released to kill a third of mankind.

Read Revelation 9:15 Using Other Translations

And the four angels were loosed, which were prepared for an hour, and a day, and a month, and a year, for to slay the third part of men.
So the four angels, who had been prepared for the hour, the day, the month, and the year, were released to kill a third of mankind.
Then the four angels who had been prepared for this hour and day and month and year were turned loose to kill one-third of all the people on earth.