Trying to track the date when a user is added to certain groups or when he is removed from the group. I don't think windchill is storing this information. Any ideas?
You'll need to enable group membership auditing, then you can see group changes in the Security Audit logs:
You can give it a try by the Auditrecord functionality.
Make sure the edit group is enabled and then you will be able to extract the information for the same.