Hi nalawalla. I’m sorry to inform you that there isn’t a simple way to do this. This feature has been requested before and is being considered by our product team. 

I do have a workaround for you to play with but it isn’t foolproof and is a somewhat manual. You can set meeting buffers in each event type. This should go a long way here for your example of a single 4 hour meeting being the only event you want scheduled that day. You could set a buffer for four hours on either side of that meeting. That would mean that no one could book that meeting if you have any others that day or vice versa. Just be aware of how you set up your available hours in your event type because buffers will take that into account.

You will likely need to combine this with Book Over Meetings. With this feature you can identify specific meetings for Calendly to ignore as conflicts for certain event types. Using buffers carefully in combination with our Book Over Meeting feature should get you most of the way there.You may still be some manual grooming of your schedule though. 

More about Meeting Buffers → How to use Buffers

More about Book Over Meetings → Book Over Meetings