USPS overnight shipping usually means Priority Mail Express , and the deadline is not one fixed national time—it depends on the specific post office or acceptance location. In practice, many locations have a late afternoon cutoff, often around 5:30 PM to 6:00 PM, but you should treat that as location-dependent rather than guaranteed.

What to do

  • Check the exact cutoff time for the post office or retail counter you’re using.
  • If you’re using a pickup or drop box, make sure the package is accepted before that location’s express cutoff.
  • For the safest same-day send, arrive earlier than the posted deadline.

Important note

USPS says shipping speed and service standards depend on the service and destination, so the most reliable answer is the local acceptance time for Priority Mail Express. If you need it sent today, assume the cutoff may be earlier than the counter’s closing time.