At the beginning, it could be kind of confusing, but practice makes perfect!
For hours, we use Korean number system.
For minutes, we use Chinese number system.
I am sorry.. but I can't tell you why it is this way..
I can only assume that since Chinese number system has higher numbers than Korean ones.
Therefore, minutes will be used in Chinese as there are 60 minutes,
and hours will be used in Korean as there are 12 hours
when you generally tell the time.
Hope this helps you to remember which number system to use.
In Korean, hour is '시' and minute is '분'.
When you use Korean numbers for hours, you see hour '시' as a counting unit,
meaning that you need to shorten the numbers from 1-4 and 20.
If you don't understand this part, plese study the counting unit page first.
'am'(오전) and 'pm'(오후) are used before the time while there are used after in English.
When it's 30 mins, you can say '반 ' (half)or '삼십분'.
If you want to tell the time as '3 to 5' for 2:55 in English,
you can say '세시 오분 전'(3 hour 5 minutes
before) in Korean.