How can i make a program that reads the date(hour,minutes,seconds) then it subs it from the second date

I have a task to create a program where the user gives the Hour, Minute, Second, then he gives an other Hour,Minute,Second then the program should substract the second date from the first one.

I have been trying to not use the date format, but i cant get it to work.

The date have to be in a 24h format, and these two dates have to be in the same day. So if i write 12:59:59 then i couldnt set the second date to 12:59:58 just 13:00:00.