you got me curious and turned out Korea before modern age used a different time system like picrel. it's called '12시100각법'. In English it'd be something like '12 units 100 subdivisions method.' basically a day was divided in 12 units, a unit was divided in two subunits, and a subunit had 4 major subdivisions and 1 minor subdivisions.
but this system was only used during day, and during night a different system was used which I was too lazy to read what it was. picrel is the time system for day.
and in 1653, the government reformed the daytime system to be 12 units and 96 subdivisions, where a subunit would only have 4 major subdivisions and no minor subdivision. in this reformed system one subdivision equals 15 minutes, and one subunit equals 1 hour.