Calendar - Booking hour constraint


I want to constraint my user the hours of the day he can and cannot book a certain activity. For example, he has already something at 8am, 11 am and 2pm so, he cannot book at any time between those hours.

The main thing is that I want to tell bubble to see if the time he wants to book the activity is at least 3 hours in between already booked activities.

Hopefully this makes sense. Thanks for your help!!