In computing any period of time prescribed or allowed by the rules in this Title, HCM does not count the day of the act, or event, from which the period of time begins to run. But, HCM does include the last day of the period unless it is a Saturday, Sunday, legal holiday as defined by the Oklahoma Statutes, or any other day HCM does not remain open until 4:00 p.m. In this case, the period shall run through the end of the next day HCM is open until 4:00 p.m. The Administrator may extend any time period established by the rules in this Title.
Okla. Admin. Code § 260:25-29-10