From version 22.2.4, There is the added ability for custom field(s) located on Appointment and Time Entries to be displayed within Professional calendar views.
This is very useful if you have additional information you need to store against appointments and/or time entries.
Setup the custom field to be available in TimeTrak via Admin Console.
Against Professional user TimeTrak Profiles on the Customizations tab there is the ability to add custom fields with a tag of Time Entry or Appointment.
I.e. {TimeEntry:X_TTC_Notes}