Can I file patent applications on weekends or federal holidays?

The USPTO is not open for filing correspondence on Saturdays, Sundays, or federal holidays within the District of Columbia. However, there are exceptions:

• Correspondence deposited as Priority Mail Express® with the USPS in accordance with 37 CFR 1.10 is considered filed on the date of deposit, even on weekends or holidays
• Electronic filing systems may be available 24/7, but the official filing date will be the next business day

MPEP 510 cites 37 CFR 1.6(a)(1): “The Patent and Trademark Office is not open for the filing of correspondence on any day that is a Saturday, Sunday or Federal holiday within the District of Columbia.”