(a) All time periods in this part that are stated in terms of days are calendar days unless otherwise stated.

(b) A document shall be deemed timely if it is received or postmarked before the expiration of the applicable filing period, or, in the absence of a legible postmark, if it is received by mail within five days of the expiration of the applicable filing period.

(c) The time limits in this part are subject to waiver, estoppel and equitable tolling.

(d) The first day counted shall be the day after the event from which the time period begins to run and the last day of the period shall be included, unless it falls on a Saturday, Sunday or Federal holiday, in which case the period shall be extended to include the next business day.