(a) In computing any period of time prescribed or allowed by this subpart, the date of the act, event, default, notice or order after which the designated period of time begins to run is not to be included in the computation. The last day of the period so computed is to be included unless it is a Saturday, Sunday, or legal holiday for the FAA, in which event the period runs until the end of the next day which is neither a Saturday, Sunday nor a legal holiday.