If an applicant is added to an application, is the waiting period 7 days from LE delivery to the new applicant to close, OR is it treated as a changed circumstance requiring only a 4 day waiting period.

Since an LE only has to be delivered to one of the primary applicants, I am not sure there is such a requirement to give them a copy or wait any period of time. If you made them withdraw the current application and start over, then the normal wait times would be required.