Primasius of Hadrumetum
John gradually, by a fitting expression, foretells the four times during which the persecution will continue, namely three years and six months. Therefore he said, "for the hour and day and month and year."
A day is gradually completed by hours, months by days, and, of course, years by months. He uses the expression "prepared" to indicate the character of the devil and his angels.
They wage unceasing war against the Church of Christ and constantly desire to harm her. Yet the divine power does not permit them to harm her as much as they wish.
Rightly he had said earlier of the locusts that they were "like horses prepared for war" (Rev 9:7). For now, when he says that the angels were released, he says that he sees horses.