The unbookable period is the amount of notice you need for a client booking. This is used to prevent clients making short notice online bookings.
You can specify the amount of advance notice your business requires in order to accept a booking. The unbookable period can range from 0 hours (off) up to one week.
If you set an unbookable period of 2 hours and the current time is 2:00pm the client will be prevented from making a booking until 4:00pm.
This restriction only applies to the public booking views, not to your private Business Dashboard.