Time issues with planning

So, where I work I get my roster mailed to me every week. What I like to do is click on that time and date and make it an activity in my agenda, but when the time goes beyond 12 pm it still somehow doubles it's count within the 24 hour cycle.

For example, when i have to work from 23:30 to 6:30 it will say from 23:30 to 18:30.

Except for me being able to fix this manually each time I don't know to how to fix this.

Hopefully someone will be abke to help me out here.

Thanks in advance,