35 U.S.C. §21(b).

When the day, or the last day, for taking any action or paying any fee in the United States Patent and Trademark Office falls on Saturday, Sunday, or a Federal holiday within the District of Columbia, the action may be taken, or the fee paid, on the next succeeding secular or business day.

37 C.F.R. §2.196. Times for taking action: Expiration on Saturday, Sunday or Federal Holiday.

Whenever periods of time are specified in this part in days, calendar days are intended. When the day, or the last day fixed by statute or by regulation under this part for taking any action or paying any fee in the Office falls on a Saturday, Sunday, or Federal holiday within the District of Columbia, the action may be taken, or the fee paid, on the next succeeding day that is not a Saturday, Sunday, or a Federal holiday.

(See also 37 C.F.R. §2.145(d) for time for appeal to court and civil action.)

Any action or fee that is due on a date falling on a Saturday, Sunday, or a Federal holiday within the District of Columbia is considered timely if the action is received, or the fee paid, on the following day that is not a Saturday, Sunday, or a Federal holiday within the District of Columbia. This applies to all documents, whether filed electronically or, if permitted, on paper (see TMEP §301.01).

The following days are Federal holidays in the District of Columbia, under 5 U.S.C. §6103:

1. New Year’s Day, January 1.
2. Birthday of Martin Luther King, Jr., the third Monday in January.
3. Washington’s Birthday, the third Monday in February.
4. Memorial Day, the last Monday in May.
5. Juneteenth National Independence Day, June 19.
6. Independence Day, July 4.
7. Labor Day, the first Monday in September.
8. Columbus Day, the second Monday in October.
9. Veterans Day, November 11.
10. Thanksgiving Day, the fourth Thursday in November.
11. Christmas Day, December 25.
12. Inauguration Day (January 20 of each fourth year after 1965), except when it falls on a Saturday (see Note below).

As to the observance of holidays that fall on Saturday, 5 U.S.C. §6103 also provides:

1. (b)(1) Instead of a holiday that occurs on a Saturday, the Friday immediately before is a legal public holiday....

NOTE: If Inauguration Day (January 20 of each fourth year after 1965) falls on a Saturday, the preceding Friday is not a legal public holiday for purposes of 35 U.S.C. §21(b). When Inauguration Day falls on Sunday, the next succeeding day selected for the public observance of the inauguration of the President is a legal public holiday. 5 U.S.C. §6103(c).