Calendar

The calendar used in the Grand human Union is the Earth centric Gregorian Calendar which is still used at Rome during the diaspora period. It is based on the birth of Christ as calculated by the monk Dionysius Exiguusin in 525 A.D. This is the official dating method used by both the Church and the civil government. Many worlds also have a local date which is dependent upon local planetary orbit and world rotation, but this is not used by the civil government of the Union.
A dual day system is used by most local populations. In space, and in any other place where the local day is not reasonably applicable to human living cycles, a 24 hour day based on Roman Standard Time is used. This is 1 hr after Greenwich Mean Time aka Coordinated Universal Time.
Anywhere a reasonable local day exists (typically defined as a day between 20 and 30 hrs long,) that day is used with the local day divided into temporal hours made up of varying amounts of minutes, based on the actual astronomical length of the local day.
The Church divides the day based on the ancient liturgical hours, which are only loosely tied to exact hours. For Roman Standard Days the times are the traditional time. For local days the periods between each liturgical hour are lengthened or shortened as needed. The exact designated times are set by the local ordinary.
Those times are the traditional times as set by the Church. The Angelus is prayed three times a day, at 6 am, noon and 6 pm. It is typically marked by the triple stroke repeated three times of the Angelus Bell. It is traditional for the morning Angelus to be prayed with Lauds (morning prayer) and for the evening Angelus to be prayed with Vespers.
Other Hours are Matins or the Office of Readings, which has no specific time and Compline, which is the last prayer of the day.
Hours are typically rung at religious houses and at parishes. The Legion similarly marks the hours, at least in the non-minority units.