Okla. Stat. tit. 41 § 61
The time within which an act is to be done, as provided for in Title 41 of the Oklahoma Statutes, shall be computed by excluding the first day and including the last day. If the last day is a legal holiday as defined by Section 82.1 of Title 25 of the Oklahoma Statutes, it shall be excluded. The provisions of this section are hereby declared to be a clarification of the law as it existed prior to the effective date of this act and shall not be considered or construed to be a change of the law as it existed prior to the effective date of this act. Any action or proceeding arising under Title 41 of the Oklahoma Statutes prior to the effective date of this act for which a determination of the period of time prescribed by this section is in question or has been in question due to the enactment of Section 20, Chapter 293, O.S.L. 1999, shall be governed by the method for computation of time as prescribed by this section.
Okla. Stat. tit. 41, § 61