Setting session availability to account for lunch

I offer 4-hour organizing sessions and would like to have my clients book their sessions via scheduler. My hours are 8:00 am-6:00 pm. I want to avoid sessions being scheduled starting at 10:00 or 11:00 - because I don’t want to add in a lunch break. When I enter 8:00 am - 1:00 pm  and 12:00-6:00 pm for availability I cannot save because the times overlap. Basically, I’d like sessions to begin ONLY at 8:00, 9:00, and 12:00 -2:00. Has anyone figured a way to set this up?