The list of twelve Horae representing the twelve hours of the day is recorded only in Late Antiquity, by Nonnus. The first and twelfth of the Horae were added to the original set of ten:

Auge (first light)
Anatole (sunrise)]
Mousike (morning hour of music and study)
Gymnastike (morning hour of exercise)
Nymphe (morning hour of ablutions)
Mesembria (noon)
Sponde (libations poured after lunch)
Elete (prayer)
Akte (eating and pleasure)
Hesperis (start of evening)
Dysis (sunset)
Arktos (night sky)

Middle Ages
Medieval astronomers such as al-Biruni and Sacrobosco,   divided the hour into 60 minutes, each of 60 seconds; this derives from Babylonian astronomy, where the corresponding terms denoted the time required for the Suns apparent motion through the ecliptic to describe one minute or second of arc, respectively. In present terms, the Babylonian degree of time was thus four minutes long, the "minute" of time was thus four seconds long and the "second" 1/15 of a second.) In medieval Europe, the Roman hours continued to be marked on sundials but the more important units of time were the canonical hours of the Orthodox and Catholic Church. During daylight, these followed the pattern set by the three-hour bells of the Roman markets, which were succeeded by the bells of local churches. They rang prime at about 6 am, terce at about 9 am, sext at noon, nones at about 3 pm, and vespers at either 6 pm or sunset. Matins and lauds precede these irregularly in the morning hours; compline follows them irregularly before sleep; and the midnight office follows that.
An hour (symbol: h; also abbreviated hr) is a unit of time conventionally reckoned as 1⁄24 of a day and scientifically reckoned between 3,599 and 3,601 seconds, depending on the speed of Earths rotation. There are 60 minutes in an hour, and 24 hours in a day. The hour was initially established in the ancient Near East as a variable measure of 1⁄12 of the night or daytime. Such seasonal, temporal, or unequal hours varied by season and latitude. Equal or equinoctial hours were taken as 1⁄24 of the day as measured from noon to noon; the minor seasonal variations of this unit were eventually smoothed by making it 1⁄24 of the mean solar day. Since this unit was not constant due to long term variations in the Earths rotation, the hour was finally separated from the Earths rotation and defined in terms of the atomic or physical second. In the modern metric system, hours are an accepted unit of time defined as 3,600 atomic seconds. However, on rare occasions an hour may incorporate a positive or negative leap second, making it last 3,599 or 3,601 seconds, in order to keep it within 0.9 seconds of UT1, which is based on measurements of the mean solar day. Name
Hour is a development of the Anglo-Norman houre and Middle English ure, first attested in the 13th century.It displaced tide tīd, "time" and stound stund, span of time.