I'd like to be able to block out certain slots for non-website bookings

Hey guys,

You'll be pleased to know we're launching this website on Friday, which is very exciting. But I still need your help with some things before the end of the week.

First of all, we'd like to block out (so no bookings can be made), all the available slots between now and the end of April. **Note, this website contains custom code in the mu-plugins file that has allowed us to achieve the booking time slots that are showing, so please base your answer on this. Can you tell me how I'd do this?

Thank you, Phil.