(a) An application filed with the board after the final filing date announced for an examination shall not be considered for such examination.

(b) Whenever the final filing date announced for an examination falls upon a Saturday, Sunday or holiday, it shall be extended to the next business day following.

(c) If an application is filed with the board through the United States mail, it shall be deemed filed on the date shown by the post office cancellation mark stamped on the envelope containing it, or on the date mailed if satisfactory proof is made that the mailing occurred on an earlier date.