As referenced in Article 8, sections 4 and 5, of the USPS-NALC and USPS-APWU national agreements, the December period (during which penalty overtime regulations are not applicable) consists of 4 consecutive service weeks.
This year, the December period begins Pay Period 25-19, Week 2 (November 30, 2019) and ends Pay Period 01-20, Week 1 (December 27, 2019).
— Labor Relations Policies and Programs,
Labor Relations, 10-10-19
Source: USPS