40 CFR 124.20: Computation of time.

(a) Any time period scheduled to begin on the occurrence of an act or event shall begin on the day after the act or event.

(b) Any time period scheduled to begin before the occurrence of an act or event shall be computed so that the period ends on the day before the act or event.

(c) If the final day of any time period falls on a weekend or legal holiday, the time period shall be extended to the next working day.

(d) When a party or interested person may or must act within a prescribed period after being served and service is made by U.S. mail, EPA's internal mail, or reliable commercial delivery service, 3 days shall be added to the prescribed time. The prescribed period for acting after being served is not expanded by 3 days when service is made by personal delivery, facsimile, or email.