Okla. Stat. tit. 58, § 622

A. Except when the executor or administrator is the petitioner or one of the petitioners, notice of the application shall be given to the executor or administrator by personal service. Notice of the application shall be given to all heirs, devisees and legatees of the decedent by mail. Notice shall be in the form required by the court and shall be given not less than ten (10) days prior to the date set by the court for the hearing on the application. B. Notice shall not be required if the application notice is waived in writing by all of the heirs, devisees and legatees of the decedent as determined pursuant to the provisions of Section 240 of this title.