(a) In computing any period of time prescribed or allowed by the rules of this part, the date of the act, event, or default after which the designated period of time begins to run, is not to be included. The last day of the period so computed is to be included, unless it is a Saturday, Sunday or a Federal legal holiday, in which event the period runs until the end of the next day which is neither a Saturday, Sunday nor a Federal legal holiday. When the period of time prescribed, or allowed, is less than 7 days, intermediate Saturdays, Sundays and holidays shall be excluded from the computations. Whenever a party has the right or is required to do some act or take some other proceedings within a prescribed period after service of a notice or other paper upon the Secretary or a party and the notice is served upon him by mail, 3 days shall be added to the prescribed period: Provided, however, That 3 days shall not be added if any extension of such time may have been granted.

(b) When these rules require the filing of any paper, such document must be received by the Secretary or a party before the close of business of the last day of the time limit, if any, for such filing or extension of time that may have been granted.