“In the NYPD, one day is divided into three 8-hour and 35-minute shifts: 11:15 PM to 7:50 AM (called a 12 to 8), 7:05 AM to 3:40 PM (called an 8 to 4) and 3:00 PM to 11:35 PM (called a 4 to 12). Officers work 5 of these shifts per week.”
From here: NYPD Profile - NYJobSource.com
Doesn’t quite explain the line in the show, though.