In the Joseon Dynasty, A day divided into 100 gak (刻, approximately a quarter) or 12 Sijin (時辰, double hours) that was composed of half-Sijin as Cho (初, beginnings of double hours) and Jeong (正, mid-points double hours). The timekeeping system was changed from 100 gak to 96 gak with using $sh{acute{i}}xi{grave{a}}n$ calendar (時憲曆) in 1654. And then 12 Sijin was changed to the 24-hours system in the same manner as current with the enforcement of the solar calendar (太陽曆) in 1896. We examine the record of the timekeeping system and notation of hours from the astronomical almanacs and official gazettes during 50 years after 1896. The Korean Empire Government first adopted the standard meridian of the Gyeongseong (former name of the Seoul in Korea) in 1908. However the mean solar time was applied to the almanac since 1913. After 1896, the year of enforcement of the solar calendar, the expression of times on a Korean almanac was written with O-jeon (午前, morning) and O-hu (午後, afternoon). The definition of 1day 24-hours system was first stated by the legislation in 1900. The expression of times was used 24 hours without O-jeon and O-hu in 1916. In daily life, the 24-hours system has used in parallel with 12-hours system divided into morning and afternoon even today.