Charles H. Spurgeon on Psalms 81:3

In the time appointed. The word rendered the time appointed, signifies the hidden or covered period; that is, the time when the moon is concealed or covered with darkness. This day was a joyful festival, returning every month; but the first day of the seventh moon was most solemn of the whole; being not only the first of the moon, but of the civil year. This was called the feast of trumpets, as it was celebrated by the blowing of trumpets from sunrising to sun setting; according to the command, "It shall be a day of the blowing of trumpets to you." This joy was a memorial of the joy of creation, and the joy of giving the law; it also preindicated the blowing of the gospel trumpet, after the dark, the covered period of the death of Christ, when the form of the church changed, and the year of the "redeemed" began; and finally, it prefigured the last day, when the trumpet of God shall sound, and the dead shall be raised. Alexander Pirie.