Availability options issue

Hi, I'm using MS Booking to create timeslots for induction sessions for students. I can't seem to block out lunchtime, even though I've defined custom availability hours of 9am-1pm and 2pm-5pm.

I'd swear this was working a couple of weeks ago when I set the dates.

I've got General Availability set to none, and Time Increments set to 30mins.