This question is about US Post Office.
USPS work hours are different for each employee. Postmasters' shifts have the most variation, as they work in four to eight-hour blocks at different times of the day and night. They can work Monday through Saturday. Common postmaster shifts include:
4 am - 8 am
5 am - 9 am
6 am - 2 pm
7 am - 3 pm
8 am - 4 pm
12 pm - 8 pm
2 pm - 8 pm
3 pm - 8 pm
4 pm - 8 pm
A mail processing clerk has shifts that begin early in the morning at 3 am and gets off usually around 7 am, sometimes later.
Mail sorters work five to six days a week, never on Sundays, and keep shifts in the 7 am - 5 pm range.
Most other positions at the Post Office keep standard hours, Monday through Friday, with certain Holidays off, from 8 am - 5 pm.