Protest window
In short
Forty-five days from receipt of the proposed assessment to file a written appeal. After it, the assessment stands.
In full
A taxpayer who disagrees with an audit's findings has forty-five days from the receipt date of the proposed assessment to file a timely appeal. An appeal form accompanies the assessment, the protest must be in writing, and it must state the reasons the assessment, tax, interest or penalties are incorrect.
The same period appears in the statute from the other direction. A.R.S. § 42-1108(B) makes the deficiency final forty-five days after receipt of the notice unless an appeal is taken, so the window and the finality are one event described twice.
Receipt starts it. Mailing does not.
Two situations are outside the window entirely. A nonaudit adjustment under § 42-1108(F) is not a deficiency assessment and may not be protested or appealed as one, however wrong it looks. And a Voluntary Disclosure agreement is final by its terms, which is the trade the program makes for its limited look-back.
A Managed Audit keeps the right to protest the results, which is one of the ways it differs from a voluntary disclosure.
A.R.S. § 42-1108(B), (F); ADOR TPT Audit; ADOR Disclosure and Compliance Programs