Calendar years used to begin in the spring with March (approximately) being the first month, which places the first day of the 7th month at the midpoint of the year. The blowing of trumpets represents an alarm sounding. Concerning end time prophesy, Daniel 9:27 says the abomination of desolation occurs at the midpoint of the week, or 3.5 years into the 7 year period. Approximately 500 years after Daniel, Jesus said this same event, as written by Daniel, initiates the Great Tribulation and the Antichrist's war against the saints. So, it makes sense that there might be a blowing of trumpets as an alarm.