29 C.F.R. § 102.2 – Time requirements for filings with the Agency.

(a) Time computation. In computing any period of time prescribed or allowed by these Rules, the day 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 legal holiday, in which event the period runs until the next Agency business day. When the period of time prescribed or allowed is less than 7 days, intermediate Saturdays, Sundays, and holidays are be excluded in the computation. Except as otherwise provided, in computing the period of time for filing a responsive document, the designated period begins to run on the date the preceding document was required to be received by the Agency, even if the preceding document was filed prior to that date.
(b) Timeliness of filings. If there is a time limit for the filing of a motion, brief, exception, request for extension of time, or other paper in any proceeding, such document must be received by the Board or the officer or agent designated to receive such matter on or before the last day of the time limit for such filing or the last day of any extension of time that may have been granted. Non E-Filed documents must be received before the official closing time of the receiving office (see www.nlrb.gov setting forth the official business hours of the Agency's several offices). E-Filed documents must be received by 11:59 p.m. of the time zone of the receiving office. In construing this section of the Rules, the Board will accept as timely filed any document which is postmarked on the day before (or earlier than) the due date; documents which are postmarked on or after the due date are untimely. “Postmarking” must include timely depositing the document with a delivery service that will provide a record showing that the document was given to the delivery service in sufficient time for delivery by the due date, but in no event later than the day before the due date. However, the following documents must be received on or before the last day for filing:
1. (1) Charges filed pursuant to Section 10(b) of the Act (see also § 102.14).
2. (2) Applications for awards and fees and other expenses under the Equal Access to Justice Act.
3. (3) Petitions to revoke subpoenas.
4. (4) Requests for extensions of time to file any document for which such an extension may be granted.
(c) Extension of time to file. Except as otherwise provided, a request for an extension of time to file a document must be filed no later than the date on which the document is due. Requests for extensions of time filed within 3 days of the due date must be grounded upon circumstances not reasonably foreseeable in advance. Requests for extension of time must be in writing and must be served simultaneously on the other parties. Parties are encouraged to seek agreement from the other parties for the extension, and to indicate the other parties' position in the extension of time request. An opposition to a request for an extension of time should be filed as soon as possible following receipt of the request.
(d) Late-filed documents.
1. (1) The following documents may be filed within a reasonable time after the time prescribed by these Rules only upon good cause shown based on excusable neglect and when no undue prejudice would result:
  1. (i) In unfair labor practice proceedings, motions, exceptions, answers to a complaint or a backpay specification, and briefs; and
  2. (ii) In representation proceedings, exceptions, requests for review, motions, briefs, and any responses to any of these documents.
2. (2) A party seeking to file such documents beyond the time prescribed by these Rules must file, along with the document, a motion that states the grounds relied on for requesting permission to file untimely. The specific facts relied on to support the motion must be set forth in affidavit form and sworn to by individuals with personal knowledge of the facts. The time for filing any document responding to the untimely document will not commence until the date a ruling issues accepting the untimely document. In addition, cross-exceptions are due within 14 days, or such further period as the Board may allow, from the date a ruling issues accepting the untimely filed documents.