Calculate overtime outside core hours

Hello, I'm very new at this so I hope I make myself very clear. I'm creating a timesheet for each employee where it shows the time in each day and time out each day with a lunch break. What I'm having trouble is with calculating any overtime done by staff outside of the core hours of business. Our business operates Monday to Friday with the core hours being 06:00-20:00 each day with regular hours of 7.6 hours per day. I've attached a copy of my timesheet for anyone's comment on how I can do this. As you will see an average day of work would be 8:30 to 17:00 with 55 minutes for lunch. What I need is the extra time worked within the core hours and the overtime outside the core hours.

Thanks,