Blocks of 3 hours, with 2 hour break

I rent a rehearsal studio in blocks of 3 hours. I start at 09:00 in the morning and have a break from 18:00 till 20:00. After diner I go on from 20:00 till 23:00.

So I need to set 3 blocks of 3 hours (between 09:00 and 18:00) BEFORE the break and 1 block of 3 hours (between 20:00 and 23:00) AFTER the break. I set the time base to 180 minutes (3 hours) in the back end. But at the front end everything is ok until 18:00… after that A+ counts from 18:00 – 21:00 and 21:00 – 0:00…

How do I properly configure this?