If you are using Time Block Scheduling, you may want to Enable a setting which causes Appointment Time to automatically adopt the earliest time in the Time Block. If this Setting is not Enabled, the system will allow you to Save an Appointment without a Time.
Only the System Administrator User will be able to access this setting.
Navigate to Setup
Custom Settings > Public System Settings
Be sure "Time Block Update Appointment Time" is checked (TRUE).
Save your changes
Next, create a new Appointment and select a Time Block. You will see the Appointment Time auto-populate prior to saving the record.
NOTE: If this setting is Disabled, and you do not select an Appointment Time, you will see the following pop-up message:
"WARNING: The Appointment 'Time' falls outside of the selected 'Time Block. Continue?"
You can click OK to Save the Appointment without a Time selected. Or, click Cancel to enter a specific Time for the Appointment.