Summary:
User Defined Fields are custom fields that can be used to collect information specific to your organization, other than the standard columns or fields available in Web TimeSheet. These fields or columns can also be made mandatory, so users will have to fill in these fields before submitting timesheet or adding new Projects etc.

Solution:
In Web TimeSheet, User defined fields added under Projects category will only be available under Project Structure and not directly visible when we edit the Project.
This is to apply the attributes of a Project to all its task and sub tasks. This will help utilize the User Defined Field at each level of a Project and its working as designed.