I hope that I'd like to customize Preview of Monthly Calendar.

Detail:
1) Go to calendar entity
2) change Calendar Views "Month".
3) Create new appointment.

?Time(Start Time/End Time) + Subect?<= by design

Enhancements:
I want to customize a format as follows

Example
1) ?Subject + Time?
2) About Time, I'd like to display "Start Time" Only

Nothing which I can edit in neither "Activity Tab (from Set Personal Option)" nor "Calendar Tab (from System Setting)"