Buffer time or bleed/margin field for tasks

Specifically for appointments and events I have to travel to, it would be nice to have a buffer or preparation time field. So if book club is at 6:30 but I have to leave at 6 to be there on time, that can be reflected on the timeline. It could look like a shadow, or translucent part of the task bleeding before/after the event itself.

This would also be great for built-in buffer time between tasks to discourage scheduling things back-to-back all day.