Until i saw people excluding the AM/PM. What does 6:30-2:30 mean? Are you working -4 hours? Are you working from 18:30 to 2:30 or from 6:30 to 14:30? Why do people choose this time format?

No, this is what is confusing you. It's like you never had any simple education, or you're completely unaware of your surroundings.

How is it possible to be so confused about clocks?