The user facing this issue is currently logged in as a substitute user for another user. The substitute user clicks the Settings button at top right corner to edit the user preferences of the other user in-order to add additional substitute users for this other user and doesn't finds the Substitute Users option in the left pane, under the Settings category, as opposed to what is normally available for all users under their respective Edit User Preferences screen.
The Substitute Users option is not available to the user who substitutes for the other user, even when the other user has granted Full Access to the substitute user on the user's profile.
Either log in as the actual user using the user's login credentials and then add the additional substitute users. Review the references section below for more information or log in as the Web TimeSheet administrator to add additional substitute users to the user profile. Review the references section below for more information.
Refer to the Related Items section in this knowledge base below, for more information on how to add, delete and setup substitute users in Web TimeSheet.
How do I set up a substitute user?
How to delete a substitute user?
How to delete substitute user without Administrator permission in Web Timesheet?