A.R.S. § 43-1365

In the case of income received or accrued during the lifetime of a decedent, or by the decedent's estate during the period of administration, the department shall send by physical mail or e-mail notices proposing to assess the tax and shall commence any proceeding in court without assessment for the collection of the tax within eighteen months after the fiduciary of the estate or any other person who is liable for the tax or any portion of the tax files a written request after the return is filed. After filing the request, a fiduciary may consent in writing to waive the limitation under this section.