Since the 6th century the number and order of the hours have been fixed thus: matins, lauds, prime, terce, sext, none, vespers, compline.
Prime (6 A.M.), Terce (9 A.M.), Sext (noon) and None (3 P.M.) are called the Little Day Hours, are often said together, and are alike in character, consisting of a hymn and some sections of Ps.
Matins and Lauds (about 7.30 A.M.); Prime, Terce (High Mass), Sext, and None (about 10 A.M.); Vespers and Compline (4 P.M.); and from four to eight hours (depending on the amount of music and the number of high masses) are thus spent in choir.
Canones, and the decree in the Sext.
Timon (in Sext.
The ordinary word for twelve o'clock was middceg, midday, also the equivalent of the canonical hour "sext."