Okla. Stat. tit. 12, app 1 R. 1.3
In computing any time period as prescribed by these rules the first day shall be excluded and the last included to complete the period. When the last day of the period so computed falls on a day when the court clerk's office at which the act is to be performed or the instrument is to be filed is not open during the full business day (until 4:00 p.m.), the period shall stand extended to include the next ensuing full business day. 12 O.S. § 2006. The additional time of three (3) days granted by 12 O.S. § 2006(D) is not applicable to the time periods described in these rules, except that the three day period will apply in computing the time to file a post-trial motion in district court after having been served with the judgment, decree or final order by mail as prescribed in 12 O.S. § 990.2(C). When the period of time prescribed or allowed is less than eleven (11) days, intermediate legal holidays and any other day when the office of the Supreme Court Clerk does not remain open for business until the regularly scheduled closing time, shall be excluded from the computation.
Okla. Stat. tit. 12, app 1 R. 1.3