The United States Postal Service does not offer a standard service that allows customers to schedule a specific delivery time for their mail or packages. USPS delivery services are designed to follow established routes and schedules, which can vary based on many factors including mail volume, weather conditions, and operational considerations. However, USPS does provide options such as Priority Mail Express, which is guaranteed to arrive by a specific time in certain areas, typically overnight delivery. For those who have a time-sensitive delivery, Priority Mail Express is the best option to ensure prompt arrival. Customers can also use services like Package Intercept or Hold for Pickup, allowing a measure of flexibility in delivery and pickup but not a specific time guarantee. For more details about services and delivery options, one can explore the current USPS website which provides comprehensive information.