Deducting break from total hours worked

Hello,

I have an Excel sheet set up to automatically calculate the total hours worked for me. I enter in the time in and out, and the total hours is automatically calculated. The formula I am using for that is,

=IF(E90<D90,E90+1,E90)-D90

The cell that calculates the above formula is formatted to Time, 13:30

What I would like help with is how to deduct a half hour break from the total hours worked IF it is 6 hours or more and have it automatically calculate. I round the employee time either up to the nearest quarter or down depending whichever is closest, is there a way to have this factored in to the formula?

Thank you for your help, I very much appreciate it.