To assign a definition to create expiration rule for a user group go to :
Administration -> Groups -> Any group -> Expiration tab.
Available only to Administrator and Manager roles :
User Group rules are listed under Administration->User Expiration->Rules->User Groups where administrators can view and manage the rules:
When the rule is created on a User Group level, a warning popup with OK and Cancel buttons is displayed with the number of users that will be expired after the rule is applied.
Cancel cancels creation of the rule. It may take few minutes for a server to apply a rule if a user count is high.