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 25-17, Week 2 (December 2, 2017) and ends Pay Period 01-18, Week 1 (December 29, 2017).
— Labor Relations Policies and Programs,
Labor Relations, 10-12-17
Source: USPS