You can use passwords to restrict access to public folders, but you cannot set password expiration dates or set different passwords for each manual.
The passwords used to restrict access to public folder don't have an expiration date.
However, you can change the password manually by deleting current password and entering new one.
Please refer to the following manual on how to set up a password:
▼Manage public folder settings (Web Browser)
*You have to be a group or folder administrator/sub-administrator to change folder settings.