30 CFR §700.15

1. (a)Except as otherwise provided, computation of time under this chapter is based on calendar days.
2. (b)In computing any period of prescribed time, the day on which the designated period of time begins is not included. The last day of the period is included unless it is a Saturday, Sunday, or legal holiday on which the regulatory authority is not open for business, in which event the period runs until the end of the next day which is not a Saturday, Sunday, or legal holiday.
3. (c)Intermediate Saturdays, Sundays, and legal holidays are excluded from the computation when the period of prescribed time is 7 days or less.