NET
15 Then the four angels who had been prepared for this hour, day, month, and year were set free to kill a third of humanity.
Darby
15 And the four angels were loosed, who are prepared for the hour and day and month and year, that they might slay the third part of men;
KJV
15 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.