When the sixth trumpet blew (Rev 9), how long did the four angels prepare to kill 1/3 of the human population?

TRIV When the sixth trumpet blew (Rev 9), how long did the four angels prepare to kill 1/3 of the human population?

In that day, saith the LORD of hosts, shall ye call every man his neighbour under the vine and under the fig tree. Zechariah 3:10

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. Revelation 9:15

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