The Calendar Tile currently requires that events that appear there have their Time attribute displayed. If you uncheck the Time attribute checkbox, you receive the error message "Title and time are both required":
An improvement request has been submitted to have the Time attribute no longer be a required selection in this section. This article describes how to get more information about the status of this request.
For more information on the status of this improvement request, please contact your account executive or customer success manager, referencing the code JVPROFSVCS-356.