Your buffer times determine the amount of time Clara leaves between meetings. It is turned off by default, but you can change it in your Dashboard.
Please note that buffer time is not a visible block on your calendar, but is taken into account by Clara when determining your availability and suggesting times. You can prompt Clara to ignore this option in a meeting request. For example:
"Clara, you can suggest any open time I have this week. It's okay to ignore my buffer."
"Clara, CC'd, can help get us set. Clara, you can ignore my preferences for this call. Please suggest times in the next few days."