It would be interesting to have a configuration option which statically excludes a given single (night)time window (or alternatively provide it the other way around as an activity time window) from being displayed in the calendar UI.

Most people don't have e.g. any appointments between 11 pm and 6 am, yet it is taking up valuable screen estate.

Uncluttering the UI by just showing the relevant part of the day and save people from scrolling over always empty rows in the calendar would be a very useful feature.