All of the Church services are divided into three cycles: daily, weekly, and yearly.
The Daily Cycle of Services
The daily cycle of services are those services which are celebrated by the Holy Orthodox Church during the course of a single day. There are nine services in the full daily cycle: vespers, compline, nocturnes (midnight service), matins, first hour, third hour, sixth hour, ninth hour, and the Divine Liturgy or, in its place, Typica, otherwise called the "Pro-Liturgy Service."
Following the example of Moses who, in describing God's creation of the world, began the day with evening, the Orthodox Church begins the daily cycle with the evening service of vespers.
Vespers--is the service celebrated towards the end of the day at evening, in which we express our gratitude to God for the day which has passed.
Compline--is a service composed of the reading of a series of prayers in which we ask the Lord God for forgiveness of sins and that He grant us during sleep rest of body and soul and preserve us from the wiles of the devil.
Nocturnes, or the Midnight Service, is the service appointed to be said at midnight in remembrance of the nighttime prayer of the Saviour in the Garden of Gethsemane. This service calls the faithful to be ready at all times for the day of Judgment which will come unexpectedly, like "a bridegroom in the night," as the parable of the ten virgins relates.
Matins--is celebrated in the morning before sunrise, in this service we thank God for the night just passed, and we ask of Him mercy for the approaching day
First Hour--corresponds to the first three hours of our daytime, 6-9AM. (In ancient times, an "hour" referred to the length of a "watch" that lasted for three hours as we measure them today; each service of the daily cycle corresponds to one of these three hour divisions. ) The First Hour prayers sanctify the already breaking day.
Third Hour--corresponds to our period from 9-12 AM, It recalls the descent of the Holy Spirit upon the Apostles.
Sixth Hour--corresponds to our period from 12-3 PM and reminds us of the Crucifixion of our Lord Jesus Christ,
Ninth Hour--corresponds to our period from 3-6 PM and reminds us of the death on the Cross of our Lord.
In addition to these eight services which cover the eight three hour periods of the day, Christians celebrate every day the Divine Liturgy. This is the most central of the Divine Services. During the course of its celebration, the entire earthly life of the Saviour is brought to mind, and the Mystery of Holy Communion is accomplished in fulfillment of Christ' s command to break bread in memory of Him, a command He gave at the Last Supper. The Liturgy is celebrated in the morning before midday.
In ancient times, in monasteries and among hermits, all of these services were conducted separately at the time appointed for each. Later, for the sake of being more practical, they were combined into three groups: evening, morning and daytime. The evening services consist of Ninth Hour, Vespers and Compline; the morning services consist of Nocturnes, Matins and First Hour; the daytime services consist of Third and Sixth Hours and Liturgy or Typica.
the eve of major feasts and Sundays, Vespers, Matins and First Hour are combined
into what is called an All-night Vigil, so-called because among ancient
Christians (and in some monasteries today) this service lasted all night.
(From The Law of God by Archpriest Seraphim Slobodskoy; translated by Mrs. James Price et al.)[OA/_private/oabot.htm]