Date override in Scheduler not working

[ira_ira]

I've set up the scheduler and have managed before to set Date overrides. However, this feature seems to have stopped working. I'm just adding dates, and keeping the hours to 9 to 5, click add, see the date added, but when I navigate the scheduler page, I still see the date showing and I'm able to book an appointment. 

What am I missing? Is there a tick somewhere to make this work?