(1) In computing any period of time for acts required by any of the commission's rules, the day of the act, event, or default after which the designated period of time begins to run is not included. The last day of the period so computed is included unless it is a Saturday, Sunday, legal holiday, or the department offices are closed on such day. In that event, the period runs until the end of the next day when the department offices are open which is not one of the aforementioned days. When the period of time prescribed or allowed is less than seven days, intermediate Saturdays, Sundays and holidays are excluded in computation. A half holiday will be considered as other days and not as a holiday.

(2) Whenever a party has a right or is required to do some act under any of the commission's rules within a prescribed period after service of a notice or other paper upon the party and service is by mail, three days shall be added to the prescribed period. The date of service is computed from the date on which service is made by mail, as shown by the certificate of service or date of mailing. Service by mail is complete upon mailing.

(3) Except as to dates fixed by statute and not subject to modification, the hearing examiner or the commission may enlarge the time to perform an act. The time may be enlarged for cause shown, with or without a motion or notice, when a request for enlargement of time is made prior to the expiration of the time in which the act is to be performed. If the request is made after the expiration of the specified period in which to act, enlargement may be allowed only upon a showing of excusable neglect in the failure to act.